Leetcode#127 Word Ladder

原题地址

BFS

Word Ladder II的简化版（参见这篇文章）

由于只需要计算步数，所以简单许多。

代码：

 int ladderLength(string start, string end, unordered_set<string> &dict) {
         if (start == end)
             return ;

         unordered_set<string> old;
         queue<string> layer;
         int len = ;

         layer.push(start);
         while (!layer.empty()) {
             queue<string> nextLayer;
             while (!layer.empty()) {
                 string str = layer.front();
                 layer.pop();
                 if (str == end)
                     return len;
                 for (int i = ; i < str.length(); i++) {
                     for (char j = 'a'; j <= 'z'; j++) {
                         string next = str;
                         next[i] = j;
                         if (old.find(next) == old.end() && dict.find(next) != dict.end()) {
                             old.insert(next);
                             nextLayer.push(next);
                         }
                     }
                 }
             }
             len++;
             layer = nextLayer;
         }

         return ;
 }