链接：LintCode 炼码

class Solution {
public:
    /**
     * @param start: a string
     * @param end: a string
     * @param dict: a set of string
     * @return: An integer
     */
    int ladderLength(string &start, string &end, unordered_set<string> &dict) {
        // write your code here
        std::queue<std::string> que;
        que.push(start);
        std::unordered_map<std::string, int> distance;
        //distance.insert(std::string(start), 0);
        distance[start] = 1;
        dict.insert(end);
        auto get_next = [](std::string& f)->std::vector<std::string> {
            std::string front(f);
            std::vector<std::string> result;
            for (int i = 0; i < front.size(); ++i) {
                char tmp = front[i];
                for (char ch = 'a'; ch <= 'z'; ++ch) {
                    if (tmp == ch) {
                        continue;
                    }
                    front[i] = ch;
                    result.push_back(front);
                }
                front[i] = tmp;
            }
            return result;
        };
        while (!que.empty()) {
            auto f = que.front();
            que.pop();
            for (auto neighboard : get_next(f)) {
                if (dict.find(neighboard) == dict.end()) {
                    continue;
                }
                //cout << "neigh=" << neighboard << " ";
                if (distance.find(neighboard) != distance.end()) {
                    continue;
                }
                if (neighboard == end) {
                    return distance[f]+1;
                }
                distance[neighboard] = distance[f]+1;
                que.push(neighboard);
                
            }
            //cout << endl;
        }
        return -1;
    }
    
};

题解：