[LeetCode] 90. Subsets II

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

public class Solution {
    public List<List<Integer>> subsetsWithDup(int[] nums) {
        List<List<Integer>> results=new ArrayList<List<Integer>>();
        results.add(new ArrayList<Integer>());
        int preEnd=0;
        Arrays.sort(nums);//必须排序
        for(int i=0;i<nums.length;i++){
            int n=results.size();
            int start;
            if(i>0&&nums[i]==nums[i-1]) start=preEnd;//若有重复，则不重复添加已经添加过的子集，从preEnd开始添加
            else start=0;
            List<Integer> tmp = null;
            for(int j=start;j<n;j++){
                tmp=new ArrayList<>(results.get(j));
                tmp.add(nums[i]);
                results.add(tmp);               
            }
            preEnd=n;
        }
        return results;

    }
}