begin to write pinyin_lookup2.cpp

diff --git a/src/lookup/pinyin_lookup2.cpp b/src/lookup/pinyin_lookup2.cpp
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+++ b/src/lookup/pinyin_lookup2.cpp
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+/* 
+ *  libpinyin
+ *  Library to deal with pinyin.
+ *  
+ *  Copyright (C) 2012 Peng Wu <alexepico@gmail.com>
+ *  
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ * 
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *  GNU General Public License for more details.
+ *  
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+#include "pinyin_lookup2.h"
+#include "stl_lite.h"
+
+using namespace pinyin;
+
+/* internal definition */
+static const size_t nbeam = 32;
+
+/* populate the candidates. */
+static bool populate_candidates(/* out */ GPtrArray * candidates,
+                                /* in */ LookupStepContent step) {
+    g_ptr_array_set_size(candidates, 0);
+
+    if (0 == step->len)
+        return false;
+
+    for (size_t i = 0; i < step->len; ++i) {
+        lookup_value_t * value = &g_array_index
+            (step, lookup_value_t, i);
+
+        g_ptr_array_add(candidates, value);
+    }
+
+    return true;
+}
+
+static bool lookup_value_less_than(lookup_value_t * lhs, lookup_value_t * rhs){
+    return lhs->m_poss < rhs->m_poss;
+}
+
+/* use maximum heap to get the topest results. */
+static bool get_top_results(/* out */ GPtrArray * topresults,
+                            /* in */ GPtrArray * candidates) {
+    g_ptr_array_set_size(topresults, 0);
+
+    if (0 == candidates->len)
+        return false;
+
+    lookup_value_t ** begin =
+        (lookup_value_t **) &g_ptr_array_index(candidates, 0);
+    lookup_value_t ** end =
+        (lookup_value_t **) &g_ptr_array_index(candidates, candidates->len);
+
+    std_lite::make_heap(begin, end, lookup_value_less_than);
+
+    while (end != begin) {
+        lookup_value_t * one = *begin;
+        g_ptr_array_add(topresults, one);
+
+        std_lite::pop_heap(begin, end, lookup_value_less_than);
+        --end;
+
+        if (topresults->len >= nbeam)
+            break;
+    }
+
+    return true;
+}
+