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Permutations II⚓︎

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Description⚓︎

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

Solution⚓︎

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