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

 

对比leetcode78：

 1 public class Solution {
 2     public List<List<Integer>> subsets(int[] nums) {
 3         List<List<Integer>> subsets = new ArrayList<>();
 4         List<Integer> tempSubset = new ArrayList<>();
 5         for (int size = 0; size <= nums.length; size++) {
 6             backtracking(0, tempSubset, subsets, size, nums); // 不同的子集大小
 7         }
 8         return subsets;
 9     }
10 
11     private void backtracking(int start, List<Integer> tempSubset, List<List<Integer>> subsets,
12                               final int size, final int[] nums) {
13 
14         if (tempSubset.size() == size) {
15             subsets.add(new ArrayList<>(tempSubset));
16             return;
17         }
18         for (int i = start; i < nums.length; i++) {
19             tempSubset.add(nums[i]);
20             backtracking(i + 1, tempSubset, subsets, size, nums);
21             tempSubset.remove(tempSubset.size() - 1);
22         }
23     }
24 }