单词接龙II

class Solution {
public:
    vector<vector<string>> findLadders(string beginWord, string endWord, vector<string>& wordList) {
        unordered_set<string>dict(wordList.begin(),wordList.end());
        vector<vector<string>>ans;
        queue<vector<string>>container;
        container.push({beginWord});
        while(!container.empty()){
            unordered_set<string>hadTry;
            for(int i=container.size();i>0;i--){
                vector<string>curArr=container.front();container.pop();
                string tail=curArr.back();
                if(tail==endWord){
                    ans.push_back(curArr);
                    continue;
                }
                for(int j=0;j<tail.size();j++){
                    char tmp=tail[j];//要
                    for(char c=‘a‘;c<=‘z‘;c++){
                        if(c==tmp)continue;//原始状态
                        tail[j]=c;
                        if(!dict.count(tail))continue;//不可
                        hadTry.insert(tail);//记录，之后可删除剪枝
                        curArr.push_back(tail);//要
                        container.push(curArr);//要
                        curArr.pop_back();//不要
                    }
                    tail[j]=tmp;//不要
                }
            }
            if(ans.size())return ans;//当前层完
            for(auto &s:hadTry)dict.erase(s);
        }
        return {};
    }
};