[Leetcode] Word Ladder

class Solution {public:    int ladderLength(string start, string end, unordered_set<string> &dict) {                unordered_set<string> visited;        visited.insert(start);        queue<string> que;        int curLevel = 1;        int curLevelNum = 1;        int nextLevelNum = 0;        que.push(start);                while (!que.empty())        {            string cur = que.front();            que.pop();                        --curLevelNum;            for (unordered_set<string>::iterator it = dict.begin(); it != dict.end(); ++it)            {                string temp = *it;                if (canChange(temp, cur) && visited.find(temp) == visited.end())                {                    que.push(temp);                    visited.insert(temp);                    ++nextLevelNum;                }            }                        if (canChange(cur, end)) return curLevel + 1;                        if (curLevelNum == 0)            {                ++curLevel;                curLevelNum = nextLevelNum;                nextLevelNum = 0;                            }        }                return 0;    }        bool canChange(string a, string b)    {        if (a.size() != b.size())            return false;                int count = 0;        for (int i = 0; i < a.size(); ++i)        {            if (a[i] != b[i])                        {                if (count == 1) return false;                ++count;            }        }                return count == 0 ? false: true;    }};