LeetCode: Word Ladder

直接看答案。。

 1 class Solution {

 2 public:

 3     int ladderLength(string start, string end, unordered_set<string> &dict) {

 4         // Start typing your C/C++ solution below

 5         // DO NOT write int main() function

 6         if (start.size() != end.size() || !dict.size()) return 0;

 7         int dis = 1;

 8         queue<string> queTopush, queTopop;

 9         queTopop.push(start);

10         while (dict.size() && !queTopop.empty()) {

11             while (!queTopop.empty()) {

12                 string str = queTopop.front();

13                 queTopop.pop();

14                 for (int i = 0; i < str.size(); i++) {

15                     for (char j = 'a'; j <= 'z'; j++) {

16                         if (j == str[i]) continue;

17                         char tmp = str[i];

18                         str[i] = j;

19                         if (str == end) return dis+1;

20                         if (dict.count(str)) {

21                             queTopush.push(str);

22                             dict.erase(str);

23                         }

24                         str[i] = tmp;

25                     }

26                 }

27             }

28             queTopop.swap(queTopush);

29             dis++;

30         }

31         return 0;

32     }

33 };