# 90.Subsets-II

## 90. Subsets II

## 题目地址

<https://leetcode.com/problems/subsets-ii/>

<http://www.lintcode.com/problem/subsets-ii/description>

<https://www.jiuzhang.com/solutions/subsets/>

## 题目描述

```
Given an integer array nums that may contain duplicates, return all possible subsets (the power set).

The solution set must not contain duplicate subsets. Return the solution in any order.

Example 1:
Input: nums = [1,2,2]
Output: [[],[1],[1,2],[1,2,2],[2],[2,2]]

Example 2:
Input: nums = [0]
Output: [[],[0]]

Constraints:
1 <= nums.length <= 10
-10 <= nums[i] <= 10
```

## 代码

### Approach #1 Backtracing

```java
class Solution {
    public ArrayList<ArrayList<Integer>> subsetsWithDup(ArrayList<Integer> array) {
    ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
    if (array == null) return result;

    Collections.sort(array);

    List<Integer> list = new ArrayList<Integer>();
    dfs(array, 0, list, result);

    return result;
  }

  private void dfs(ArrayList<Integer> array, int pos, List<Integer> list, ArrayList<ArrayList<Integer>> result) {
    result.add(new ArrayList<Integer>(list));
    for (int i = pos; i < array.size(); i++) {

      // exclude duplicates
      if (i != pos && array.get(i) == array.get(i - 1)) {
        continue;
      }

      list.add(array.get(i));
      dfs(array, i + 1, list, result);
      list.remove(list.size() - 1);
    }
  }

}
```