Permutations -Leetcode

Given a collection of distinct numbers, return all possible permutations.

For example,
[1,2,3] have the following permutations:

[  [1,2,3],  [1,3,2],  [2,1,3],  [2,3,1],  [3,1,2],  [3,2,1]]

Solution

class Solution {    public List<List<Integer>> permute(int[] nums) {   List<List<Integer>> list = new ArrayList<>();   // Arrays.sort(nums); // not necessary   backtrack(list, new ArrayList<>(), nums);   return list;}private void backtrack(List<List<Integer>> list, List<Integer> tempList, int [] nums){   if(tempList.size() == nums.length){      list.add(new ArrayList<>(tempList));   } else{      for(int i = 0; i < nums.length; i++){          if(tempList.contains(nums[i])) continue; // element already exists, skip         tempList.add(nums[i]);         backtrack(list, tempList, nums);         tempList.remove(tempList.size() - 1);      }   }} }