题目：

题解：

class Solution {
public:int minMutation(string start, string end, vector<string>& bank) {int m = start.size();int n = bank.size();vector<vector<int>> adj(n);int endIndex = -1;for (int i = 0; i < n; i++) {if (end == bank[i]) {endIndex = i;}for (int j = i + 1; j < n; j++) {int mutations = 0;for (int k = 0; k < m; k++) {if (bank[i][k] != bank[j][k]) {mutations++;}if (mutations > 1) {break;}}if (mutations == 1) {adj[i].emplace_back(j);adj[j].emplace_back(i);}}}if (endIndex == -1) {return -1;}queue<int> qu;vector<bool> visited(n, false);int step = 1;for (int i = 0; i < n; i++) {int mutations = 0;for (int k = 0; k < m; k++) {if (start[k] != bank[i][k]) {mutations++;}if (mutations > 1) {break;}}if (mutations == 1) {qu.emplace(i);visited[i] = true;}}        while (!qu.empty()) {int sz = qu.size();for (int i = 0; i < sz; i++) {int curr = qu.front();qu.pop();if (curr == endIndex) {return step;}for (auto & next : adj[curr]) {if (visited[next]) {continue;}visited[next] = true;qu.emplace(next);}}step++;}return -1;}
};