[itint5]单词变换
基本上就是word ladder。直接来BFS,记录前驱。
vector<string> transform(set<string> &dict, string from, string to) { vector<string> ans; if (from.length() != to.length()) { return ans; } queue<string> que; map<string, string> prev_map; que.push(from); prev_map[from] = ""; while (!que.empty()) { string s = que.front(); que.pop(); if (s == to) break; for (int i = 0; i < s.length(); i++) { char tmp = s[i]; for (char c = 'A'; c <= 'Z'; c++) { if (tmp == c) continue; s[i] = c; if (dict.find(s) != dict.end() && prev_map.find(s) == prev_map.end()) { que.push(s); prev_map[s] = s; prev_map[s][i] = tmp; } } s[i] = tmp; } } if (prev_map.find(to) == prev_map.end()) return ans; string last = to; do { ans.push_back(last); last = prev_map[last]; } while (last != ""); for (int i = 0; i < ans.size() / 2; i++) { int k = ans.size() - i - 1; string tmp = ans[i]; ans[i] = ans[k]; ans[k] = tmp; } return ans; }