127. 单词接龙

水题，spfa即可

class Solution {
public:
    vector<int> gra[5010];
    int d[5010], vis[5010];

    bool check(string str1, string str2)
    {
        int len1 = str1.length(), len2 = str2.length();
        if(len1 != len2) return false;
        int cnt = 0;
        for(int i = 0; i < len1; i++)
        {
            if(str1[i] != str2[i]) cnt++;
            if(cnt > 1) return false;
        }
        return true;

    }


    int spfa(int s, int t)
    {
        for(int i = 0; i < 5010; i++) d[i] = 0x7fffffff;
        memset(vis, 0, sizeof(vis));
        queue<int> Q;
        Q.push(s);
        vis[s] = 1;
        d[s] = 0;
        while(!Q.empty())
        {
            
            int u = Q.front(); Q.pop();
            vis[u] = 0;
            int len = gra[u].size();
            for(int i = 0; i < len; i++)
            {
                int v = gra[u][i];
                if(d[v] > d[u] + 1)
                {
                    d[v] = d[u] + 1;
                    if(!vis[v])
                    {
                        Q.push(v);
                        vis[v] = 1;
                    }
                }

            }


        }
        if(d[t] == 0x7fffffff) return 0;
        return d[t] + 1;
    }


    int ladderLength(string beginWord, string endWord, vector<string>& wordList) {
        int n = wordList.size();
        int s = 0, t = 0;
        for(int i = 0; i < n; i++)
        {
            if(wordList[i] == beginWord) s = i + 1;
            if(wordList[i] == endWord) t = i + 1;
        }
        if(s == 0)
        {
            s = n + 1;
            wordList.push_back(beginWord);
            n = wordList.size();
        }


        for(int i = 0; i < n; i++)
        {
            for(int j = i + 1; j < n; j++)
            {
                if(check(wordList[i], wordList[j]))
                {
                    gra[i + 1].push_back(j + 1);
                    gra[j + 1].push_back(i + 1);

                }

            }
        }
        return spfa(s, t);


    }
};