LeetCode – Refresh – Word Ladder

weixin_34397291

于 2015-03-25 09:20:00 发布

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CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/shuashuashua/p/4364710.html

本文介绍了一种解决单词梯问题的算法实现。该算法使用广度优先搜索(BFS)策略，并借助哈希集合来记录已访问过的单词。通过迭代地改变起始单词中的每个字符并检查结果是否存在于字典中，最终找到到达目标单词所需的最少步骤。

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Do the BFS and use a hashset to record whether the word has been found before.

 1 class Solution {
 2 public:
 3     int ladderLength(string start, string end, unordered_set<string> &dict) {
 4         int len = start.size();
 5         if (len == 0 || len != end.size()) return 0;
 6         queue<string> q;
 7         q.push(start);
 8         unordered_set<string> record;
 9         int current = 1, future = 0, level = 1;
10         while (!q.empty()) {
11             string str = q.front();
12             q.pop(), current--;
13             for (int i = 0; i < len; i++) {
14                 string tmp = str;
15                 for (char c = 'a'; c <= 'z'; c++) {
16                     tmp[i] = c;
17                     if (tmp == end) return level+1;
18                     if (record.find(tmp) == record.end() && dict.find(tmp) != dict.end()) {
19                         record.insert(tmp);
20                         q.push(tmp);
21                         future++;
22                     }
23                 }
24             }
25             if (!current) {
26                 current = future;
27                 future = 0;
28                 level++;
29             }
30         }
31     }
32 };