# Permutations II Problem

## Description

LeetCode Problem 47.

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

Example 1:

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

Example 2:

``````1
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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

## Sample C++ Code

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class Solution {
public:
int n;
vector<vector<int>> ans;
set<vector<int>> visited;

void backtrack(int idx, vector<int>& nums) {
if (idx == n)
visited.insert(nums);

int tmp;
for (int i = idx; i < n; i ++) {
if (nums[idx] == nums[i] && i != idx)
continue;

tmp = nums[idx];
nums[idx] = nums[i];
nums[i] = tmp;

backtrack(idx+1, nums);

tmp = nums[idx];
nums[idx] = nums[i];
nums[i] = tmp;
}
}
vector<vector<int>> permuteUnique(vector<int>& nums) {
n = nums.size();

backtrack(0, nums);

for (auto x : visited)
ans.push_back(x);
return ans;
}
};
``````