LeetCode-Word Ladder

可以转化成图的题目，bfs，代码可以写得很短！

class Solution {
public:
    int ladderLength(string start, string end, unordered_set<string> &dict) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        deque<pair<string, int> > nodes;
        nodes.push_back(pair<string, int>(start, 1));
        while (!nodes.empty()) {
            pair<string, int> node = nodes.front();
            nodes.pop_front();
            string word = node.first;
            int len = node.second;
            for (size_t i = 0; i < word.size(); ++i) {
                char old = word[i];
                for (char c = 'a'; c <= 'z'; ++c) {
                    word[i] = c;
                    if (word == end)
                        return (len + 1);
                    if (dict.find(word) != dict.end()) {
                        nodes.push_back(pair<string, int>(word, len + 1));
                        dict.erase(word);
                    }
                }
                word[i] = old;
            }
        }
        return 0;
    }
};