5道经典深度优先搜索与宽度优先搜索相关题目-词语阶梯

class Solution {
public:
    int ladderLength(string beginWord, string endWord, vector<string>& wordList) {
        unordered_set<string> dict(wordList.begin(), wordList.end());
        if(!dict.count(endWord)) return 0;
        int res=1,n=beginWord.size();
        unordered_set<string> q1{{beginWord}}, q2{{endWord}};
        dict.erase(beginWord);
        while(!q1.empty() && !q2.empty()){
            ++res;
            unordered_set<string> q;
            for(const string& w:q1){
                string cur = w;
                for(int i=0;i<n;++i){
                    char old=cur[i];
                    for(char c='a'; c<='z'; ++c){
                        cur[i]=c;
                        if(q2.count(cur)){
                            return res;
                        } else if(dict.count(cur)){
                            q.insert(cur);
                            dict.erase(cur);
                        }
                    }
                    cur[i] = old;
                }
            }
            swap(q,q1);
            if(q1.size() > q2.size()){
                swap(q1, q2);
            }
        }
        return 0;
    }
};