Leetcode 127 Solution

class Solution {
public:
    int ladderLength(string beginWord, string endWord, unordered_set<string>& wordList) {
        queue<string> q;
        q.push(beginWord);

        wordList.erase(beginWord);

        int step = 1;

        while (q.empty() == false)
        {
            int s = q.size();
            step++;

            for (int i = 0; i < s; i++)
            {
                auto str = q.front();
                q.pop();

                for (int j = 0; j < str.size(); j++)
                {
                    for (char ch = 'a'; ch <= 'z'; ch++)
                    {
                        if (ch == str[j])
                            continue;

                        char oldch = str[j];
                        str[j] = ch;

                        if (str == endWord)
                            return step;

                        if (wordList.find(str) != wordList.end())
                        {
                            wordList.erase(str);
                            q.push(str);
                        }

                        str[j] = oldch;
                    }
                }
            }
        }

        return 0;
    }
};