46. Permutations

 1 class Solution {
 2     List<List<Integer>> res = new ArrayList<>();
 3     public List<List<Integer>> permute(int[] nums) {
 4         backtrack(nums, new ArrayList<>());
 5         return res;
 6     }
 7     
 8     public void backtrack(int[] nums, List<Integer> list) {
 9         if(list.size() == nums.length) {
10             res.add(new ArrayList<>(list));
11         }
12         for(int i = 0; i < nums.length; i++) {
13             if(list.contains(nums[i])) continue;
14             list.add(nums[i]);
15             backtrack(nums, list);
16             list.remove(list.size() - 1);
17         }
18     }   
19 }