LeetCode – Refresh – Word Ladder

Do the BFS and use a hashset to record whether the word has been found before.

class Solution {
public:
    int ladderLength(string start, string end, unordered_set<string> &dict) {
        int len = start.size();
        if (len == 0 || len != end.size()) return 0;
        queue<string> q;
        q.push(start);
        unordered_set<string> record;
        int current = 1, future = 0, level = 1;
        while (!q.empty()) {
            string str = q.front();
            q.pop(), current--;
            for (int i = 0; i < len; i++) {
                string tmp = str;
                for (char c = 'a'; c <= 'z'; c++) {
                    tmp[i] = c;
                    if (tmp == end) return level+1;
                    if (record.find(tmp) == record.end() && dict.find(tmp) != dict.end()) {
                        record.insert(tmp);
                        q.push(tmp);
                        future++;
                    }
                }
            }
            if (!current) {
                current = future;
                future = 0;
                level++;
            }
        }
    }
};