class Solution {
public:
    int ladderLength(string beginWord, string endWord, vector<string>& wordList) {

       int n = (int)wordList.size();

        if( !n ) return 0;

        unordered_set<string>st;
        unordered_map<string, int>mp;
        mp[beginWord] = 1;

        for( string s: wordList )
        {
            st.insert(s);
        }

        queue<string>q;
        q.push(beginWord);

        int depth = 0;

        while( !q.empty() )
        {
             depth++;
            int sz = q.size();

            for( int i=0;i<sz;i++)
            {
                string word = q.front(); q.pop();

                if( word == endWord ) return depth;

                int m = (int)word.size();
                for(int j=0; j<m; j++)
                {
                    char temp = word[j];

                    for( char c = 'a'; c<='z'; c++)
                    {
                        word[j] = c;
                        if(st.find(word) == st.end() || mp[word])
                        {
                            continue;
                        }
                        q.push(word);
                        mp[word] = 1;
                    }

                    word[j] = temp;
                }



            }

        }



        return 0;

    }
};