一、题目

Given a collection of numbers, nums, that might contain duplicates, return all possible unique permutations in any order.

Example 1:

Input: nums = [1,1,2]
Output:
[[1,1,2],
[1,2,1],
[2,1,1]]
Example 2:

Input: nums = [1,2,3]
Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

Constraints:

1 <= nums.length <= 8
-10 <= nums[i] <= 10

二、题解

class Solution {
public:vector<int> path;vector<vector<int>> res;void backtracking(vector<int>& nums,vector<int>& used){if(path.size() == nums.size()){res.push_back(path);return;}for(int i = 0;i < nums.size();i++){if(i > 0 && nums[i] == nums[i-1] && used[i-1] == 0) continue;if(used[i] == 1) continue;path.push_back(nums[i]);used[i] = 1;backtracking(nums,used);path.pop_back();used[i] = 0;}}vector<vector<int>> permuteUnique(vector<int>& nums) {sort(nums.begin(),nums.end());vector<int> used(nums.size(),0);backtracking(nums,used);return res;}
};