leetcode47

 1 public class Solution {
 2     public List<List<Integer>> permuteUnique(int[] nums) {
 3         List<List<Integer>> permutes = new ArrayList<>();
 4         List<Integer> permuteList = new ArrayList<>();
 5         Arrays.sort(nums);  // 排序
 6         boolean[] hasVisited = new boolean[nums.length];
 7         backtracking(permuteList, permutes, hasVisited, nums);
 8         return permutes;
 9     }
10 
11     private void backtracking(List<Integer> permuteList, List<List<Integer>> permutes, boolean[] visited, final int[] nums) {
12         if (permuteList.size() == nums.length) {
13             permutes.add(new ArrayList<>(permuteList));
14             return;
15         }
16 
17         for (int i = 0; i < visited.length; i++) {
18             if (i != 0 && nums[i] == nums[i - 1] && !visited[i - 1]) {
19                 continue;  // 防止重复
20             }
21             if (visited[i]){
22                 continue;
23             }
24             visited[i] = true;
25             permuteList.add(nums[i]);
26             backtracking(permuteList, permutes, visited, nums);
27             permuteList.remove(permuteList.size() - 1);
28             visited[i] = false;
29         }
30     }
31 }

对比leetcode46：

 1 public class LEET_46 {
 2     public List<List<Integer>> permute(int[] nums) {
 3         List<List<Integer>> permutes = new ArrayList<>();
 4         List<Integer> permuteList = new ArrayList<>();
 5         boolean[] hasVisited = new boolean[nums.length];
 6         backtracking(permuteList, permutes, hasVisited, nums);
 7         return permutes;
 8     }
 9 
10     private void backtracking(List<Integer> permuteList, List<List<Integer>> permutes, boolean[] visited, final int[] nums) {
11         if (permuteList.size() == nums.length) {
12             permutes.add(new ArrayList<>(permuteList)); // 重新构造一个 List
13             return;
14         }
15         for (int i = 0; i < visited.length; i++) {
16             if (visited[i]) {
17                 continue;
18             }
19             visited[i] = true;
20             permuteList.add(nums[i]);
21             backtracking(permuteList, permutes, visited, nums);
22             permuteList.remove(permuteList.size() - 1);
23             visited[i] = false;
24         }
25     }
26 }