Problem: Permutation II

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

class Solution {
    public List<List<Integer>> permuteUnique(int[] nums) {
   HashMap<Integer,Boolean> visited = new HashMap<>();
        for(int i = 0; i < nums.length; i++){
            visited.put(i,false);
        }
        List<Integer> list = new ArrayList<>();
        List<List<Integer>> ans = new ArrayList();
        helper(nums,visited,0,nums.length,list,ans);
        return ans;
    }

    private void helper(int[] nums,HashMap<Integer,Boolean> map,int i, int n, List<Integer> list,List<List<Integer>> ans){

        if(i == n){
            ans.add(new ArrayList<>(list));
            return;
        }
        HashSet<Integer> set = new HashSet();
        for(int j = 0; j < n; j++){

            if(map.get(j) == false){
                if(set.contains(nums[j]))continue;
                list.add(nums[j]);
                map.put(j,true);
                set.add(nums[j]);
                helper(nums, map, i+1, n, list,ans);
                list.remove(list.size()-1);
                map.put(j,false);
            }
        }

    }

}