LeetCode-90 Subsets II

Given a collection of integers that might contain duplicates, S, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

 

For example,
If S = [1,2,2], a solution is:

[
  [2],
  [1],
  [1,2,2],
  [2,2],
  [1,2],
  []
]


本题与上一题“Subsets”的思路相同，不过在选择元素的时候需要将同一位置重复重现的元素排除。见代码中标注的地方。

List<List<Integer>> lists = new ArrayList<List<Integer>>();
public List<List<Integer>> subsetsWithDup(int[] nums) {
    Arrays.sort(nums);
    for(int i=0; i<=nums.length; i++) {
        subsets(nums, 0, i, new ArrayList<Integer>());
    }
    return lists;
}

private void subsets(int[] nums, int start, int count, List<Integer> list) {
    if(list.size() == count) {
        lists.add(new ArrayList<Integer>(list));
    } else {
        for(int i=start; i<nums.length; i++) {
            if(i > start && nums[i] == nums[i-1]) continue;
            list.add(nums[i]);
            subsets(nums, i+1, count, list);
            list.remove(list.size()-1);
        }
    }
}