[leetcode 127]Word Ladder

Given two words (start and end), and a dictionary, find the length of shortest transformation sequence from start to end, such that:

1. Only one letter can be changed at a time
2. Each intermediate word must exist in the dictionary

For example,

Given:
start = "hit"
end = "cog"
dict = ["hot","dot","dog","lot","log"]

As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog",
return its length 5.

Note:

• Return 0 if there is no such transformation sequence.
• All words have the same length.

• All words contain only lowercase alphabetic characters.

class Solution {public:    int ladderLength(string start, string end, unordered_set<string> &dict) {        if (start.size() == 0 || end.size() == 0) {            return 0;        }        if (start.size() != end.size()) {            return 0;        }        vector<string> path;        int level = 1;        int count = 1;        path.push_back(start);        dict.erase(start);        while (!path.empty()) {            auto tmp = path.front();            path.erase(path.begin());            count--;            for (int j = 0; j < tmp.size(); j++) {                auto ms = tmp;                for (auto i = 'a'; i < 'z'; i++) {                    if (i == ms[j]) {                        continue;                    }                    ms[j] = i;                    if (ms == end) {                        return level+1;                    }                    if (dict.find(ms) != dict.end()) {                        path.push_back(ms);                        dict.erase(ms);                    }                }            }            if (count == 0) {                count = path.size();                level++;            }                    }        return 0;    }};