Permutations II

Leetcode 47.

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class Solution {
    public List<List<Integer>> permuteUnique(int[] nums) {
     int numsLength = nums.length;
     List<List<Integer>> ans = new ArrayList<>();
     List<Integer> list = new ArrayList<Integer>(); 
     if(numsLength == 1){
        list.add(nums[0]);   
        ans.add(list);
        return ans; 
     }
     boolean[] visited = new boolean[numsLength];
     
     Arrays.sort(nums);
     backtricking(nums,ans,list,visited);
     return ans;
   }
   public void backtricking(int[] nums, List<List<Integer>> ans,List<Integer> list,boolean[] visited){
       //recursion stop condition 
       if(list.size() == nums.length){
        //collect the results
         ans.add(new ArrayList<>(list));
         return;
       }

       //for loop for this layer 
       for(int i = 0; i < nums.length;i++){
           //avoid the duplicate cases
           if(i != 0 && nums[i] == nums[i - 1] && !visited[i - 1])
             continue;
           //avoid elements that have already been passed 
           if(visited[i])
             continue;
           
           visited[i] = true;
           list.add(nums[i]);
           //recursion 
           backtricking(nums,ans,list,visited);
           //undo the previous operation 
           list.remove(list.size() - 1);
           visited[i] = false;
       }

   }

}