[leetcode]Word Ladder

一次只允许变动一个字符,然后得到目标字符串最少步数.

我们把每个合法字符看成一个点,之间的变化看成边,那么就是个图,就是球start到end的最短路.

用BFS就可以了...

class Solution {
public:
    int ladderLength(string start, string end, unordered_set<string> &dict) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(start == end) return 1;
        queue<string > que;
        map<string , int> dist;
        dist[start] = 0;
        que.push(start);
        while(!que.empty()){
            string top = que.front();que.pop();
            for(int i = 0 ; i < top.length() ; i++){
                for(int j = 'a' ; j <= 'z' ; j++){
                    if(j != top[i]){
                        string next = top;
                        next[i] = j;
                        if(next == end){
                            return dist[top] + 2;
                        }
                        if(dict.find(next) != dict.end() && dist.find(next) == dist.end()){
                            dist[next] = dist[top] + 1;
                            que.push(next);
                        }
                    }
                }
            }
        }
        return 0;
    }
};