LeetCode 46: Permutations

 1 public class Solution {
 2     public List<List<Integer>> permute(int[] nums) {
 3         List<List<Integer>> result = new ArrayList<>();
 4         result.add(new ArrayList<>());
 5         
 6         for (int i = 0; i < nums.length; i++) {
 7             List<List<Integer>> newResult = new ArrayList<>();
 8             for (List<Integer> internal : result) {
 9                 for (int j = 0; j <= i; j++) {
10                     List<Integer> newInternal = new ArrayList<>(internal);
11                     newInternal.add(j, nums[i]);
12                     newResult.add(newInternal);
13                 }
14             }
15             result = newResult;
16         }
17         return result;
18     }
19 
20 }

 1 public class Solution {
 2     public List<List<Integer>> permute(int[] nums) {
 3         List<List<Integer>> result = new ArrayList<>();
 4         DFS(result, new ArrayList<>(), nums, new boolean[nums.length]);
 5         return result;
 6     }
 7     
 8     private void DFS(List<List<Integer>> result, List<Integer> currentList, int[] nums, boolean[] visited) {
 9         if (currentList.size() == nums.length) {
10             result.add(new ArrayList<>(currentList));
11             return;
12         }
13         
14         for (int i = 0; i < nums.length; i++) {
15             if (visited[i]) {
16                 continue;
17             }
18             visited[i] = true;
19             currentList.add(nums[i]);
20             DFS(result, currentList, nums, visited);
21             currentList.remove(currentList.size() - 1);
22             visited[i] = false;
23         }
24     }
25 }