doc/html/heap/concepts.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>Concepts &amp; Interface</title>
   5 <link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css">
   6 <meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
   7 <link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
   8 <link rel="up" href="../heap.html" title="Chapter&#160;13.&#160;Boost.Heap">
   9 <link rel="prev" href="../heap.html" title="Chapter&#160;13.&#160;Boost.Heap">
  10 <link rel="next" href="data_structures.html" title="Data Structures">
  11 </head>
  12 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
  13 <table cellpadding="2" width="100%"><tr>
  14 <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td>
  15 <td align="center"><a href="../../../index.html">Home</a></td>
  16 <td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td>
  17 <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
  18 <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
  19 <td align="center"><a href="../../../more/index.htm">More</a></td>
  20 </tr></table>
  21 <hr>
  22 <div class="spirit-nav">
  23 <a accesskey="p" href="../heap.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../heap.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="data_structures.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
  24 </div>
  25 <div class="section">
  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="heap.concepts"></a><a class="link" href="concepts.html" title="Concepts &amp; Interface">Concepts &amp; Interface</a>
  28 </h2></div></div></div>
  29 <div class="toc"><dl class="toc">
  30 <dt><span class="section"><a href="concepts.html#heap.concepts.basic">Basic Priority Queue Interface</a></span></dt>
  31 <dt><span class="section"><a href="concepts.html#heap.concepts.iterators">Priority Queue Iterators</a></span></dt>
  32 <dt><span class="section"><a href="concepts.html#heap.concepts.comparing">Comparing Priority Queues &amp;
  33       Equivalence</a></span></dt>
  34 <dt><span class="section"><a href="concepts.html#heap.concepts.merge">Merging Priority Queues</a></span></dt>
  35 <dt><span class="section"><a href="concepts.html#heap.concepts.mutability">Mutability</a></span></dt>
  36 <dt><span class="section"><a href="concepts.html#heap.concepts.stability">Stability</a></span></dt>
  37 </dl></div>
  38 <div class="section">
  39 <div class="titlepage"><div><div><h3 class="title">
  40 <a name="heap.concepts.basic"></a><a class="link" href="concepts.html#heap.concepts.basic" title="Basic Priority Queue Interface">Basic Priority Queue Interface</a>
  41 </h3></div></div></div>
  42 <p>
  43         Priority queues are queues of objects, that are ordered by their priority.
  44         They support the operations of adding nodes to the data structure, accessing
  45         the top element (the element with the highest priority), and removing the
  46         top element.
  47       </p>
  48 <div class="note"><table border="0" summary="Note">
  49 <tr>
  50 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
  51 <th align="left">Note</th>
  52 </tr>
  53 <tr><td align="left" valign="top"><p>
  54           <code class="literal">boost.heap</code> implements priority queues as max-heaps to
  55           be consistent with the STL heap functions. This is in contrast to the typical
  56           textbook design, which uses min-heaps.
  57         </p></td></tr>
  58 </table></div>
  59 <h6>
  60 <a name="heap.concepts.basic.h0"></a>
  61         <span class="phrase"><a name="heap.concepts.basic.synopsis"></a></span><a class="link" href="concepts.html#heap.concepts.basic.synopsis">Synopsis</a>
  62       </h6>
  63 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="special">...</span><span class="identifier">Options</span><span class="special">&gt;</span>
  64 <span class="keyword">class</span> <span class="identifier">priority_queue</span>
  65 <span class="special">{</span>
  66     <span class="comment">// types</span>
  67     <span class="keyword">typedef</span> <span class="identifier">T</span>                   <span class="identifier">value_type</span><span class="special">;</span>
  68     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">size_type</span><span class="special">;</span>
  69     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">difference_type</span><span class="special">;</span>
  70
  71     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">allocator_type</span><span class="special">;</span>
  72     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">value_compare</span><span class="special">;</span>
  73
  74     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">reference</span><span class="special">;</span>
  75     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">const_reference</span><span class="special">;</span>
  76     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">pointer</span><span class="special">;</span>
  77     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">const_pointer</span><span class="special">;</span>
  78
  79     <span class="comment">// construct/copy/destruct</span>
  80     <span class="keyword">explicit</span> <span class="identifier">priority_queue</span><span class="special">(</span><span class="identifier">value_compare</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="special">=</span> <span class="identifier">value_compare</span><span class="special">());</span>
  81     <span class="identifier">priority_queue</span><span class="special">(</span><span class="identifier">priority_queue</span> <span class="keyword">const</span> <span class="special">&amp;);</span>
  82     <span class="identifier">priority_queue</span><span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">priority_queue</span> <span class="keyword">const</span> <span class="special">&amp;);</span>
  83     <span class="identifier">priority_queue</span><span class="special">(</span><span class="identifier">priority_queue</span> <span class="special">&amp;&amp;);</span>                  <span class="comment">// move semantics (C++11 only)</span>
  84     <span class="identifier">priority_queue</span><span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">priority_queue</span> <span class="special">&amp;&amp;);</span>       <span class="comment">// move semantics (C++11 only)</span>
  85
  86     <span class="comment">// public member functions</span>
  87     <span class="emphasis"><em>unspecified</em></span> <span class="identifier">push</span><span class="special">(</span><span class="identifier">const_reference</span><span class="special">);</span>                  <span class="comment">// push new element to heap</span>
  88     <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Args</span> <span class="special">&amp;&amp;...);</span>   <span class="comment">// push new element to heap, C++11 only</span>
  89     <span class="identifier">const_reference</span> <span class="identifier">top</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>                        <span class="comment">// return top element</span>
  90     <span class="keyword">void</span> <span class="identifier">pop</span><span class="special">();</span>                                         <span class="comment">// remove top element</span>
  91     <span class="keyword">void</span> <span class="identifier">clear</span><span class="special">();</span>                                       <span class="comment">// clear heap</span>
  92     <span class="identifier">size_type</span> <span class="identifier">size</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>                             <span class="comment">// number of elements</span>
  93     <span class="keyword">bool</span> <span class="identifier">empty</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>                                 <span class="comment">// priority queue is empty</span>
  94     <span class="identifier">allocator_type</span> <span class="identifier">get_allocator</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>           <span class="comment">// return allocator</span>
  95     <span class="identifier">size_type</span> <span class="identifier">max_size</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>                     <span class="comment">// maximal possible size</span>
  96     <span class="keyword">void</span> <span class="identifier">reserve</span><span class="special">(</span><span class="identifier">size_type</span><span class="special">);</span>                            <span class="comment">// reserve space, only available if (has_reserve == true)</span>
  97
  98     <span class="comment">// heap equivalence</span>
  99     <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">HeapType</span><span class="special">&gt;</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">==(</span><span class="identifier">HeapType</span> <span class="keyword">const</span> <span class="special">&amp;)</span> <span class="keyword">const</span><span class="special">;</span>
 100     <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">HeapType</span><span class="special">&gt;</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!=(</span><span class="identifier">HeapType</span> <span class="keyword">const</span> <span class="special">&amp;)</span> <span class="keyword">const</span><span class="special">;</span>
 101
 102     <span class="comment">// heap comparison</span>
 103     <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">HeapType</span><span class="special">&gt;</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&lt;(</span><span class="identifier">HeapType</span> <span class="keyword">const</span> <span class="special">&amp;)</span> <span class="keyword">const</span><span class="special">;</span>
 104     <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">HeapType</span><span class="special">&gt;</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&gt;(</span><span class="identifier">HeapType</span> <span class="keyword">const</span> <span class="special">&amp;)</span> <span class="keyword">const</span><span class="special">;</span>
 105     <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">HeapType</span><span class="special">&gt;</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&gt;=(</span><span class="identifier">HeapType</span> <span class="keyword">const</span> <span class="special">&amp;)</span> <span class="keyword">const</span><span class="special">;</span>
 106     <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">HeapType</span><span class="special">&gt;</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&lt;=(</span><span class="identifier">HeapType</span> <span class="keyword">const</span> <span class="special">&amp;)</span> <span class="keyword">const</span><span class="special">;</span>
 107
 108     <span class="comment">// public data members</span>
 109     <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">constant_time_size</span><span class="special">;</span>               <span class="comment">// size() has constant complexity</span>
 110     <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">has_ordered_iterators</span><span class="special">;</span>            <span class="comment">// priority queue has <a class="link" href="concepts.html#heap.concepts.iterators" title="Priority Queue Iterators">ordered iterators</a></span>
 111     <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">is_mergable</span><span class="special">;</span>                      <span class="comment">// priority queue is efficiently <a class="link" href="concepts.html#heap.concepts.merge" title="Merging Priority Queues">mergable</a></span>
 112     <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">is_stable</span><span class="special">;</span>                        <span class="comment">// priority queue has a <a class="link" href="concepts.html#heap.concepts.stability" title="Stability">stable heap order</a></span>
 113     <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">has_reserve</span><span class="special">;</span>                      <span class="comment">// priority queue has a reserve() member</span>
 114 <span class="special">};</span>
 115 </pre>
 116 <h6>
 117 <a name="heap.concepts.basic.h1"></a>
 118         <span class="phrase"><a name="heap.concepts.basic.example"></a></span><a class="link" href="concepts.html#heap.concepts.basic.example">Example</a>
 119       </h6>
 120 <p>
 121 </p>
 122 <pre class="programlisting"><span class="comment">// PriorityQueue is expected to be a max-heap of integer values</span>
 123 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">&gt;</span>
 124 <span class="keyword">void</span> <span class="identifier">basic_interface</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span>
 125 <span class="special">{</span>
 126     <span class="identifier">PriorityQueue</span> <span class="identifier">pq</span><span class="special">;</span>
 127
 128     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">2</span><span class="special">);</span>
 129     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">3</span><span class="special">);</span>
 130     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
 131
 132     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Priority Queue: popped elements"</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 133     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">top</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 3</span>
 134     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">pop</span><span class="special">();</span>
 135     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">top</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 2</span>
 136     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">pop</span><span class="special">();</span>
 137     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">top</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 1</span>
 138     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">pop</span><span class="special">();</span>
 139     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 140 <span class="special">}</span>
 141 </pre>
 142 <p>
 143       </p>
 144 </div>
 145 <div class="section">
 146 <div class="titlepage"><div><div><h3 class="title">
 147 <a name="heap.concepts.iterators"></a><a class="link" href="concepts.html#heap.concepts.iterators" title="Priority Queue Iterators">Priority Queue Iterators</a>
 148 </h3></div></div></div>
 149 <div class="toc"><dl class="toc"><dt><span class="section"><a href="concepts.html#heap.concepts.iterators.ordered_iterators">Ordered
 150         Iterators</a></span></dt></dl></div>
 151 <h6>
 152 <a name="heap.concepts.iterators.h0"></a>
 153         <span class="phrase"><a name="heap.concepts.iterators.synopsis"></a></span><a class="link" href="concepts.html#heap.concepts.iterators.synopsis">Synopsis</a>
 154       </h6>
 155 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">iteratable_heap_interface</span>
 156 <span class="special">{</span>
 157 <span class="keyword">public</span><span class="special">:</span>
 158     <span class="comment">// types</span>
 159     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">iterator</span><span class="special">;</span>
 160     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">const_iterator</span><span class="special">;</span>
 161     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span>         <span class="identifier">ordered_iterator</span><span class="special">;</span>
 162
 163     <span class="comment">// public member functions</span>
 164     <span class="identifier">iterator</span> <span class="identifier">begin</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
 165     <span class="identifier">iterator</span> <span class="identifier">end</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
 166     <span class="identifier">ordered_iterator</span> <span class="identifier">ordered_begin</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
 167     <span class="identifier">ordered_iterator</span> <span class="identifier">ordered_end</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
 168 <span class="special">};</span>
 169 </pre>
 170 <p>
 171         Priority queues provide iterators, that can be used to traverse their elements.
 172         All heap iterators are const_iterators, that means they cannot be used to
 173         modify the values, because changing the value of a heap node may corrupt
 174         the heap order. Details about modifying heap nodes are described in the section
 175         about the <a class="link" href="concepts.html#heap.concepts.mutability" title="Mutability">mutability interface</a>.
 176       </p>
 177 <p>
 178         Iterators do not visit heap elements in any specific order. Unless otherwise
 179         noted, all non-const heap member functions invalidate iterators, while all
 180         const member functions preserve the iterator validity.
 181       </p>
 182 <div class="note"><table border="0" summary="Note">
 183 <tr>
 184 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
 185 <th align="left">Note</th>
 186 </tr>
 187 <tr><td align="left" valign="top"><p>
 188           Some implementations require iterators, that contain a set of elements,
 189           that are <span class="bold"><strong>discovered</strong></span>, but not <span class="bold"><strong>visited</strong></span>. Therefore copying iterators can be inefficient
 190           and should be avoided.
 191         </p></td></tr>
 192 </table></div>
 193 <h6>
 194 <a name="heap.concepts.iterators.h1"></a>
 195         <span class="phrase"><a name="heap.concepts.iterators.example"></a></span><a class="link" href="concepts.html#heap.concepts.iterators.example">Example</a>
 196       </h6>
 197 <p>
 198 </p>
 199 <pre class="programlisting"><span class="comment">// PriorityQueue is expected to be a max-heap of integer values</span>
 200 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">&gt;</span>
 201 <span class="keyword">void</span> <span class="identifier">iterator_interface</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span>
 202 <span class="special">{</span>
 203     <span class="identifier">PriorityQueue</span> <span class="identifier">pq</span><span class="special">;</span>
 204
 205     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">2</span><span class="special">);</span>
 206     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">3</span><span class="special">);</span>
 207     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
 208
 209     <span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">begin</span> <span class="special">=</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">begin</span><span class="special">();</span>
 210     <span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">end</span> <span class="special">=</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">end</span><span class="special">();</span>
 211
 212     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Priority Queue: iteration"</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 213     <span class="keyword">for</span> <span class="special">(</span><span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">it</span> <span class="special">=</span> <span class="identifier">begin</span><span class="special">;</span> <span class="identifier">it</span> <span class="special">!=</span> <span class="identifier">end</span><span class="special">;</span> <span class="special">++</span><span class="identifier">it</span><span class="special">)</span>
 214         <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="special">*</span><span class="identifier">it</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 1, 2, 3 in unspecified order</span>
 215     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 216 <span class="special">}</span>
 217 </pre>
 218 <p>
 219       </p>
 220 <div class="section">
 221 <div class="titlepage"><div><div><h4 class="title">
 222 <a name="heap.concepts.iterators.ordered_iterators"></a><a class="link" href="concepts.html#heap.concepts.iterators.ordered_iterators" title="Ordered Iterators">Ordered
 223         Iterators</a>
 224 </h4></div></div></div>
 225 <p>
 226           Except for <code class="computeroutput"><a class="link" href="../boost/heap/priority_queue.html" title="Class template priority_queue">boost::heap::priority_queue</a></code>
 227           all <code class="literal">boost.heap</code> data structures support ordered iterators,
 228           which visit all elements of the heap in heap-order. The implementation
 229           of these <code class="literal">ordered_iterator</code>s requires some internal bookkeeping,
 230           so iterating the a heap in heap order has an amortized complexity of O(N*log(N)).
 231         </p>
 232 <h6>
 233 <a name="heap.concepts.iterators.ordered_iterators.h0"></a>
 234           <span class="phrase"><a name="heap.concepts.iterators.ordered_iterators.example"></a></span><a class="link" href="concepts.html#heap.concepts.iterators.ordered_iterators.example">Example</a>
 235         </h6>
 236 <p>
 237 </p>
 238 <pre class="programlisting"><span class="comment">// PriorityQueue is expected to be a max-heap of integer values</span>
 239 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">&gt;</span>
 240 <span class="keyword">void</span> <span class="identifier">ordered_iterator_interface</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span>
 241 <span class="special">{</span>
 242     <span class="identifier">PriorityQueue</span> <span class="identifier">pq</span><span class="special">;</span>
 243
 244     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">2</span><span class="special">);</span>
 245     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">3</span><span class="special">);</span>
 246     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
 247
 248     <span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">::</span><span class="identifier">ordered_iterator</span> <span class="identifier">begin</span> <span class="special">=</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">ordered_begin</span><span class="special">();</span>
 249     <span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">::</span><span class="identifier">ordered_iterator</span> <span class="identifier">end</span> <span class="special">=</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">ordered_end</span><span class="special">();</span>
 250
 251     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Priority Queue: ordered iteration"</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 252     <span class="keyword">for</span> <span class="special">(</span><span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">::</span><span class="identifier">ordered_iterator</span> <span class="identifier">it</span> <span class="special">=</span> <span class="identifier">begin</span><span class="special">;</span> <span class="identifier">it</span> <span class="special">!=</span> <span class="identifier">end</span><span class="special">;</span> <span class="special">++</span><span class="identifier">it</span><span class="special">)</span>
 253         <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="special">*</span><span class="identifier">it</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 3, 2, 1 (i.e. 1, 2, 3 in heap order)</span>
 254     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 255 <span class="special">}</span>
 256 </pre>
 257 <p>
 258         </p>
 259 </div>
 260 </div>
 261 <div class="section">
 262 <div class="titlepage"><div><div><h3 class="title">
 263 <a name="heap.concepts.comparing"></a><a class="link" href="concepts.html#heap.concepts.comparing" title="Comparing Priority Queues &amp; Equivalence">Comparing Priority Queues &amp;
 264       Equivalence</a>
 265 </h3></div></div></div>
 266 <p>
 267         The data structures of <code class="literal">boost.heap</code> can be compared with
 268         standard comparison operators. The comparison is performed by comparing two
 269         heaps element by element using <code class="literal">value_compare</code>.
 270       </p>
 271 <div class="note"><table border="0" summary="Note">
 272 <tr>
 273 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td>
 274 <th align="left">Note</th>
 275 </tr>
 276 <tr><td align="left" valign="top"><p>
 277           Depending on the heap type, this operation can be rather expensive, because
 278           both data structures need to be traversed in heap order. On heaps without
 279           ordered iterators, the heap needs to be copied internally. The typical
 280           complexity is O(n log(n)).
 281         </p></td></tr>
 282 </table></div>
 283 </div>
 284 <div class="section">
 285 <div class="titlepage"><div><div><h3 class="title">
 286 <a name="heap.concepts.merge"></a><a class="link" href="concepts.html#heap.concepts.merge" title="Merging Priority Queues">Merging Priority Queues</a>
 287 </h3></div></div></div>
 288 <h4>
 289 <a name="heap.concepts.merge.h0"></a>
 290         <span class="phrase"><a name="heap.concepts.merge.mergable_priority_queues"></a></span><a class="link" href="concepts.html#heap.concepts.merge.mergable_priority_queues">Mergable
 291         Priority Queues</a>
 292       </h4>
 293 <h6>
 294 <a name="heap.concepts.merge.h1"></a>
 295         <span class="phrase"><a name="heap.concepts.merge.synopsis"></a></span><a class="link" href="concepts.html#heap.concepts.merge.synopsis">Synopsis</a>
 296       </h6>
 297 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">mergable_heap_interface</span>
 298 <span class="special">{</span>
 299 <span class="keyword">public</span><span class="special">:</span>
 300     <span class="comment">// public member functions</span>
 301     <span class="keyword">void</span> <span class="identifier">merge</span><span class="special">(</span><span class="identifier">mergable_heap_interface</span> <span class="special">&amp;);</span>
 302 <span class="special">};</span>
 303 </pre>
 304 <p>
 305         <code class="literal">boost.heap</code> has a concept of a Mergable Priority Queue.
 306         A mergable priority queue can efficiently be merged with a different instance
 307         of the same type.
 308       </p>
 309 <h6>
 310 <a name="heap.concepts.merge.h2"></a>
 311         <span class="phrase"><a name="heap.concepts.merge.example"></a></span><a class="link" href="concepts.html#heap.concepts.merge.example">Example</a>
 312       </h6>
 313 <p>
 314 </p>
 315 <pre class="programlisting"><span class="comment">// PriorityQueue is expected to be a max-heap of integer values</span>
 316 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">&gt;</span>
 317 <span class="keyword">void</span> <span class="identifier">merge_interface</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span>
 318 <span class="special">{</span>
 319     <span class="identifier">PriorityQueue</span> <span class="identifier">pq</span><span class="special">;</span>
 320
 321     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">3</span><span class="special">);</span>
 322     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">5</span><span class="special">);</span>
 323     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
 324
 325     <span class="identifier">PriorityQueue</span> <span class="identifier">pq2</span><span class="special">;</span>
 326
 327     <span class="identifier">pq2</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">2</span><span class="special">);</span>
 328     <span class="identifier">pq2</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">4</span><span class="special">);</span>
 329     <span class="identifier">pq2</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>
 330
 331     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">merge</span><span class="special">(</span><span class="identifier">pq2</span><span class="special">);</span>
 332
 333     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Priority Queue: merge"</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 334     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"first queue: "</span><span class="special">;</span>
 335     <span class="keyword">while</span> <span class="special">(!</span><span class="identifier">pq</span><span class="special">.</span><span class="identifier">empty</span><span class="special">())</span> <span class="special">{</span>
 336         <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">top</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 5 4 3 2 1 0</span>
 337         <span class="identifier">pq</span><span class="special">.</span><span class="identifier">pop</span><span class="special">();</span>
 338     <span class="special">}</span>
 339     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 340
 341     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"second queue: "</span><span class="special">;</span>
 342     <span class="keyword">while</span> <span class="special">(!</span><span class="identifier">pq2</span><span class="special">.</span><span class="identifier">empty</span><span class="special">())</span> <span class="special">{</span>
 343         <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">pq2</span><span class="special">.</span><span class="identifier">top</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 4 2 0</span>
 344         <span class="identifier">pq2</span><span class="special">.</span><span class="identifier">pop</span><span class="special">();</span>
 345     <span class="special">}</span>
 346     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 347 <span class="special">}</span>
 348 </pre>
 349 <p>
 350       </p>
 351 <h4>
 352 <a name="heap.concepts.merge.h3"></a>
 353         <span class="phrase"><a name="heap.concepts.merge.heap_merge_algorithms"></a></span><a class="link" href="concepts.html#heap.concepts.merge.heap_merge_algorithms">Heap
 354         Merge Algorithms</a>
 355       </h4>
 356 <p>
 357         <code class="literal">boost.heap</code> provides a <code class="literal">heap_merge()</code>
 358         algorithm that is can be used to merge different kinds of heaps. Using this
 359         algorithm, all <code class="literal">boost.heap</code> data structures can be merged,
 360         although some cannot be merged efficiently.
 361       </p>
 362 <h6>
 363 <a name="heap.concepts.merge.h4"></a>
 364         <span class="phrase"><a name="heap.concepts.merge.example0"></a></span><a class="link" href="concepts.html#heap.concepts.merge.example0">Example</a>
 365       </h6>
 366 <p>
 367 </p>
 368 <pre class="programlisting"><span class="comment">// PriorityQueue is expected to be a max-heap of integer values</span>
 369 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">&gt;</span>
 370 <span class="keyword">void</span> <span class="identifier">heap_merge_algorithm</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span>
 371 <span class="special">{</span>
 372     <span class="identifier">PriorityQueue</span> <span class="identifier">pq</span><span class="special">;</span>
 373
 374     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">3</span><span class="special">);</span>
 375     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">5</span><span class="special">);</span>
 376     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
 377
 378     <span class="identifier">PriorityQueue</span> <span class="identifier">pq2</span><span class="special">;</span>
 379
 380     <span class="identifier">pq2</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">2</span><span class="special">);</span>
 381     <span class="identifier">pq2</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">4</span><span class="special">);</span>
 382     <span class="identifier">pq2</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>
 383
 384     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">heap</span><span class="special">::</span><span class="identifier">heap_merge</span><span class="special">(</span><span class="identifier">pq</span><span class="special">,</span> <span class="identifier">pq2</span><span class="special">);</span>
 385
 386     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Priority Queue: merge"</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 387     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"first queue: "</span><span class="special">;</span>
 388     <span class="keyword">while</span> <span class="special">(!</span><span class="identifier">pq</span><span class="special">.</span><span class="identifier">empty</span><span class="special">())</span> <span class="special">{</span>
 389         <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">top</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 5 4 3 2 1 0</span>
 390         <span class="identifier">pq</span><span class="special">.</span><span class="identifier">pop</span><span class="special">();</span>
 391     <span class="special">}</span>
 392     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 393
 394     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"second queue: "</span><span class="special">;</span>
 395     <span class="keyword">while</span> <span class="special">(!</span><span class="identifier">pq2</span><span class="special">.</span><span class="identifier">empty</span><span class="special">())</span> <span class="special">{</span>
 396         <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">pq2</span><span class="special">.</span><span class="identifier">top</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 4 2 0</span>
 397         <span class="identifier">pq2</span><span class="special">.</span><span class="identifier">pop</span><span class="special">();</span>
 398     <span class="special">}</span>
 399     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 400 <span class="special">}</span>
 401 </pre>
 402 <p>
 403       </p>
 404 </div>
 405 <div class="section">
 406 <div class="titlepage"><div><div><h3 class="title">
 407 <a name="heap.concepts.mutability"></a><a class="link" href="concepts.html#heap.concepts.mutability" title="Mutability">Mutability</a>
 408 </h3></div></div></div>
 409 <p>
 410         Some priority queues of <code class="literal">boost.heap</code> are mutable, that means
 411         the priority of their elements can be changed. To achieve mutability, <code class="literal">boost.heap</code>
 412         introduces the concept of <span class="bold"><strong>handles</strong></span>, which
 413         can be used to access the internal nodes of the priority queue in order to
 414         change its value and to restore the heap order.
 415       </p>
 416 <h6>
 417 <a name="heap.concepts.mutability.h0"></a>
 418         <span class="phrase"><a name="heap.concepts.mutability.synopsis"></a></span><a class="link" href="concepts.html#heap.concepts.mutability.synopsis">Synopsis</a>
 419       </h6>
 420 <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">mutable_heap_interface</span>
 421 <span class="special">{</span>
 422 <span class="keyword">public</span><span class="special">:</span>
 423     <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span> <span class="identifier">iterator</span><span class="special">;</span>
 424     <span class="keyword">struct</span> <span class="identifier">handle_type</span>
 425     <span class="special">{</span>
 426         <span class="identifier">value_type</span> <span class="special">&amp;</span> <span class="keyword">operator</span><span class="special">*()</span> <span class="keyword">const</span><span class="special">;</span>
 427     <span class="special">};</span>
 428
 429     <span class="keyword">static</span> <span class="identifier">handle_type</span> <span class="identifier">s_iterator_to_handle</span><span class="special">(</span><span class="identifier">iterator</span> <span class="keyword">const</span> <span class="special">&amp;);</span>
 430
 431     <span class="comment">// priority queue interface</span>
 432     <span class="identifier">handle_type</span> <span class="identifier">push</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">v</span><span class="special">);</span>
 433
 434     <span class="comment">// update element via assignment and fix heap</span>
 435     <span class="keyword">void</span> <span class="identifier">update</span><span class="special">(</span><span class="identifier">handle_type</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">handle</span><span class="special">,</span> <span class="identifier">value_type</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">v</span><span class="special">);</span>
 436     <span class="keyword">void</span> <span class="identifier">increase</span><span class="special">(</span><span class="identifier">handle_type</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">handle</span><span class="special">,</span> <span class="identifier">value_type</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">v</span><span class="special">);</span>
 437     <span class="keyword">void</span> <span class="identifier">decrease</span><span class="special">(</span><span class="identifier">handle_type</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">handle</span><span class="special">,</span> <span class="identifier">value_type</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">v</span><span class="special">);</span>
 438
 439     <span class="comment">// fix heap after element has been changed via the handle</span>
 440     <span class="keyword">void</span> <span class="identifier">update</span><span class="special">(</span><span class="identifier">handle_type</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">handle</span><span class="special">);</span>
 441     <span class="keyword">void</span> <span class="identifier">increase</span><span class="special">(</span><span class="identifier">handle_type</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">handle</span><span class="special">);</span>
 442     <span class="keyword">void</span> <span class="identifier">decrease</span><span class="special">(</span><span class="identifier">handle_type</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">handle</span><span class="special">);</span>
 443 <span class="special">};</span>
 444 </pre>
 445 <div class="warning"><table border="0" summary="Warning">
 446 <tr>
 447 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td>
 448 <th align="left">Warning</th>
 449 </tr>
 450 <tr><td align="left" valign="top"><p>
 451           Incorrect use of <code class="literal">increase</code> or <code class="literal">decrease</code>
 452           may corrupt the priority queue data structure. If unsure use <code class="literal">update</code>
 453           can be used at the cost of efficiency.
 454         </p></td></tr>
 455 </table></div>
 456 <h6>
 457 <a name="heap.concepts.mutability.h1"></a>
 458         <span class="phrase"><a name="heap.concepts.mutability.example"></a></span><a class="link" href="concepts.html#heap.concepts.mutability.example">Example</a>
 459       </h6>
 460 <p>
 461 </p>
 462 <pre class="programlisting"><span class="comment">// PriorityQueue is expected to be a max-heap of integer values</span>
 463 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">&gt;</span>
 464 <span class="keyword">void</span> <span class="identifier">mutable_interface</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span>
 465 <span class="special">{</span>
 466     <span class="identifier">PriorityQueue</span> <span class="identifier">pq</span><span class="special">;</span>
 467     <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">::</span><span class="identifier">handle_type</span> <span class="identifier">handle_t</span><span class="special">;</span>
 468
 469     <span class="identifier">handle_t</span> <span class="identifier">t3</span> <span class="special">=</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">3</span><span class="special">);</span>
 470     <span class="identifier">handle_t</span> <span class="identifier">t5</span> <span class="special">=</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">5</span><span class="special">);</span>
 471     <span class="identifier">handle_t</span> <span class="identifier">t1</span> <span class="special">=</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
 472
 473     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">update</span><span class="special">(</span><span class="identifier">t3</span><span class="special">,</span> <span class="number">4</span><span class="special">);</span>
 474     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">increase</span><span class="special">(</span><span class="identifier">t5</span><span class="special">,</span> <span class="number">7</span><span class="special">);</span>
 475     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">decrease</span><span class="special">(</span><span class="identifier">t1</span><span class="special">,</span> <span class="number">0</span><span class="special">);</span>
 476
 477     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Priority Queue: update"</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 478     <span class="keyword">while</span> <span class="special">(!</span><span class="identifier">pq</span><span class="special">.</span><span class="identifier">empty</span><span class="special">())</span> <span class="special">{</span>
 479         <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">top</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 7, 4, 0</span>
 480         <span class="identifier">pq</span><span class="special">.</span><span class="identifier">pop</span><span class="special">();</span>
 481     <span class="special">}</span>
 482     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 483 <span class="special">}</span>
 484 </pre>
 485 <p>
 486       </p>
 487 <p>
 488         Note that handles can be stored inside the <code class="literal">value_type</code>:
 489       </p>
 490 <p>
 491 </p>
 492 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">heap_data</span>
 493 <span class="special">{</span>
 494     <span class="identifier">fibonacci_heap</span><span class="special">&lt;</span><span class="identifier">heap_data</span><span class="special">&gt;::</span><span class="identifier">handle_type</span> <span class="identifier">handle</span><span class="special">;</span>
 495     <span class="keyword">int</span> <span class="identifier">payload</span><span class="special">;</span>
 496
 497     <span class="identifier">heap_data</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">):</span>
 498         <span class="identifier">payload</span><span class="special">(</span><span class="identifier">i</span><span class="special">)</span>
 499     <span class="special">{}</span>
 500
 501     <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">&lt;(</span><span class="identifier">heap_data</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">rhs</span><span class="special">)</span> <span class="keyword">const</span>
 502     <span class="special">{</span>
 503         <span class="keyword">return</span> <span class="identifier">payload</span> <span class="special">&lt;</span> <span class="identifier">rhs</span><span class="special">.</span><span class="identifier">payload</span><span class="special">;</span>
 504     <span class="special">}</span>
 505 <span class="special">};</span>
 506
 507 <span class="keyword">void</span> <span class="identifier">mutable_interface_handle_in_value</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span>
 508 <span class="special">{</span>
 509     <span class="identifier">fibonacci_heap</span><span class="special">&lt;</span><span class="identifier">heap_data</span><span class="special">&gt;</span> <span class="identifier">heap</span><span class="special">;</span>
 510     <span class="identifier">heap_data</span> <span class="identifier">f</span><span class="special">(</span><span class="number">2</span><span class="special">);</span>
 511
 512     <span class="identifier">fibonacci_heap</span><span class="special">&lt;</span><span class="identifier">heap_data</span><span class="special">&gt;::</span><span class="identifier">handle_type</span> <span class="identifier">handle</span> <span class="special">=</span> <span class="identifier">heap</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="identifier">f</span><span class="special">);</span>
 513     <span class="special">(*</span><span class="identifier">handle</span><span class="special">).</span><span class="identifier">handle</span> <span class="special">=</span> <span class="identifier">handle</span><span class="special">;</span> <span class="comment">// store handle in node</span>
 514 <span class="special">}</span>
 515 </pre>
 516 <p>
 517       </p>
 518 <h4>
 519 <a name="heap.concepts.mutability.h2"></a>
 520         <span class="phrase"><a name="heap.concepts.mutability.the_fixup_interface"></a></span><a class="link" href="concepts.html#heap.concepts.mutability.the_fixup_interface">The
 521         Fixup Interface</a>
 522       </h4>
 523 <p>
 524         There are two different APIs to support mutability. The first family of functions
 525         provides update functionality by changing the current element by assigning
 526         a new value. The second family of functions can be used to fix the heap data
 527         structure after an element has been changed directly via a handle. While
 528         this provides the user with a means to modify the priority of queue elements
 529         without the need to change their non-priority part, this needs to be handled
 530         with care. The heap needs to be fixed up immediately after the priority of
 531         the element has been changed.
 532       </p>
 533 <p>
 534         Beside an <code class="literal">update</code> function, two additional functions <code class="literal">increase</code>
 535         and <code class="literal">decrease</code> are provided, that are generally more efficient
 536         than the generic <code class="literal">update</code> function. However the user has
 537         do ensure, that the priority of an element is changed to the right direction.
 538       </p>
 539 <h6>
 540 <a name="heap.concepts.mutability.h3"></a>
 541         <span class="phrase"><a name="heap.concepts.mutability.example0"></a></span><a class="link" href="concepts.html#heap.concepts.mutability.example0">Example</a>
 542       </h6>
 543 <p>
 544 </p>
 545 <pre class="programlisting"><span class="comment">// PriorityQueue is expected to be a max-heap of integer values</span>
 546 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">&gt;</span>
 547 <span class="keyword">void</span> <span class="identifier">mutable_fixup_interface</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span>
 548 <span class="special">{</span>
 549     <span class="identifier">PriorityQueue</span> <span class="identifier">pq</span><span class="special">;</span>
 550     <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">PriorityQueue</span><span class="special">::</span><span class="identifier">handle_type</span> <span class="identifier">handle_t</span><span class="special">;</span>
 551
 552     <span class="identifier">handle_t</span> <span class="identifier">t3</span> <span class="special">=</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">3</span><span class="special">);</span>
 553     <span class="identifier">handle_t</span> <span class="identifier">t5</span> <span class="special">=</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">5</span><span class="special">);</span>
 554     <span class="identifier">handle_t</span> <span class="identifier">t1</span> <span class="special">=</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">push</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
 555
 556     <span class="special">*</span><span class="identifier">t3</span> <span class="special">=</span> <span class="number">4</span><span class="special">;</span>
 557     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">update</span><span class="special">(</span><span class="identifier">t3</span><span class="special">);</span>
 558
 559     <span class="special">*</span><span class="identifier">t5</span> <span class="special">=</span> <span class="number">7</span><span class="special">;</span>
 560     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">increase</span><span class="special">(</span><span class="identifier">t5</span><span class="special">);</span>
 561
 562     <span class="special">*</span><span class="identifier">t1</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
 563     <span class="identifier">pq</span><span class="special">.</span><span class="identifier">decrease</span><span class="special">(</span><span class="identifier">t1</span><span class="special">);</span>
 564
 565     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Priority Queue: update with fixup"</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 566     <span class="keyword">while</span> <span class="special">(!</span><span class="identifier">pq</span><span class="special">.</span><span class="identifier">empty</span><span class="special">())</span> <span class="special">{</span>
 567         <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">pq</span><span class="special">.</span><span class="identifier">top</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">" "</span><span class="special">;</span> <span class="comment">// 7, 4, 0</span>
 568         <span class="identifier">pq</span><span class="special">.</span><span class="identifier">pop</span><span class="special">();</span>
 569     <span class="special">}</span>
 570     <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
 571 <span class="special">}</span>
 572 </pre>
 573 <p>
 574       </p>
 575 <p>
 576         Iterators can be coverted to handles using the static member function <code class="literal">s_handle_from_iterator</code>.
 577         However most implementations of <code class="literal">update</code> invalidate all
 578         iterators. The most notable exception is the <code class="computeroutput"><a class="link" href="../boost/heap/fibonacci_heap.html" title="Class template fibonacci_heap">fibonacci
 579         heap</a></code>, providing a lazy update function, that just invalidates
 580         the iterators, that are related to this handle.
 581       </p>
 582 <div class="warning"><table border="0" summary="Warning">
 583 <tr>
 584 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td>
 585 <th align="left">Warning</th>
 586 </tr>
 587 <tr><td align="left" valign="top"><p>
 588           After changing the priority via a handle, the heap needs to be fixed by
 589           calling one of the update functions. Otherwise the priority queue structure
 590           may be corrupted!
 591         </p></td></tr>
 592 </table></div>
 593 </div>
 594 <div class="section">
 595 <div class="titlepage"><div><div><h3 class="title">
 596 <a name="heap.concepts.stability"></a><a class="link" href="concepts.html#heap.concepts.stability" title="Stability">Stability</a>
 597 </h3></div></div></div>
 598 <p>
 599         A priority queue is `stable', if elements with the same priority are popped
 600         from the heap, in the same order as they are inserted. The data structures
 601         provided by <code class="literal">boost.heap</code>, can be configured to be stable
 602         at compile time using the <code class="computeroutput"><a class="link" href="../boost/heap/stable.html" title="Struct template stable">boost::heap::stable</a></code>
 603         policy. Two notions of stability are supported. If a heap is configured with
 604         <span class="bold"><strong>no stability</strong></span>, the order of nodes of the
 605         same priority is undefined, if it is configured as <span class="bold"><strong>stable</strong></span>,
 606         nodes of the same priority are ordered by their insertion time.
 607       </p>
 608 <p>
 609         Stability is achieved by associating an integer version count with each value
 610         in order to distinguish values with the same node. The type of this version
 611         count defaults to <code class="literal">boost::uintmax_t</code>, which is at least
 612         64bit on most systems. However it can be configured to use a different type
 613         using the <code class="computeroutput"><a class="link" href="../boost/heap/stability_counter_type.html" title="Struct template stability_counter_type">boost::heap::stability_counter_type</a></code>
 614         template argument.
 615       </p>
 616 <div class="warning"><table border="0" summary="Warning">
 617 <tr>
 618 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td>
 619 <th align="left">Warning</th>
 620 </tr>
 621 <tr><td align="left" valign="top"><p>
 622           The stability counter is prone to integer overflows. If an overflow occurs
 623           during a <code class="literal">push()</code> call, the operation will fail and an
 624           exception is thrown. Later <code class="literal">push()</code> call will succeed,
 625           but the stable heap order will be compromised. However an integer overflow
 626           at 64bit is very unlikely: if an application would issue one <code class="literal">push()</code>
 627           operation per microsecond, the value will overflow in more than 500000
 628           years.
 629         </p></td></tr>
 630 </table></div>
 631 </div>
 632 </div>
 633 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 634 <td align="left"></td>
 635 <td align="right"><div class="copyright-footer">Copyright &#169; 2010, 2011 Tim Blechmann<p>
 636         Distributed under the Boost Software License, Version 1.0. (See accompanying
 637         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 638       </p>
 639 </div></td>
 640 </tr></table>
 641 <hr>
 642 <div class="spirit-nav">
 643 <a accesskey="p" href="../heap.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../heap.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="data_structures.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
 644 </div>
 645 </body>
 646 </html>