47. Permutations II

class Solution {
    public List<List<Integer>> permuteUnique(int[] nums) {
    List<List<Integer>> result = new ArrayList<>();
    Arrays.sort(nums);
    helper(nums, result, new ArrayList<>(), new boolean[nums.length]);
    return result;
}

private void helper(int [] nums, List<List<Integer>> result, List<Integer> current, boolean [] used){
   if(current.size() == nums.length){
       result.add(new ArrayList<>(current));
       return;
   }

   for(int i = 0; i < nums.length; i++){
       if(used[i]) {
           continue;
       }
       used[i] = true;
       current.add(nums[i]);
        helper(nums, result, current, used);

        current.remove(current.size() - 1);
        used[i] = false;

        // Check for duplicates & skip it
        // index + 1 < nums.length to avoid array out of bound error 
        while(i + 1 < nums.length && nums[i] == nums[i + 1]){
            i++;
        }
   }
}
}