题目：

题解：

class Solution {
public:void backtrack(vector<vector<int>>& res, vector<int>& output, int first, int len){// 所有数都填完了if (first == len) {res.emplace_back(output);return;}for (int i = first; i < len; ++i) {// 动态维护数组swap(output[i], output[first]);// 继续递归填下一个数backtrack(res, output, first + 1, len);// 撤销操作swap(output[i], output[first]);}}vector<vector<int>> permute(vector<int>& nums) {vector<vector<int> > res;backtrack(res, nums, 0, (int)nums.size());return res;}
};