打印一个含有重复元素数组的所有子集

打印一个含有重复元素数组的所有子集。例如：[1,2,2]的所有子集为[[],[1],[1,2],[1,2,2],[2],[2,2]]。

1、递归求解

List<List> list=new ArrayList<List>();
    public List<List> subsetsWithDup(int[] nums) {
        List list1=new ArrayList();
        Arrays.sort(nums);
        backTrack(0,nums,list1);
        return list;
    }

    public void backTrack(int i,int[] nums,List currentList){
        list.add(currentList);
        for(int j=i;jif(j==i || nums[j]!=nums[j-1]){
                currentList.add(nums[j]);
                backTrack(j+1,nums,new ArrayList(currentList));
                currentList.remove(currentList.size()-1);
            }
        }
    }

2、直接求解

public List> subsetsWithDup(int[] nums) {
        List> res = new ArrayList<>();
        List temp = new ArrayList<>();
        res.add(temp);
        Arrays.sort(nums);
        int l = 0, k;
        for (int i = 0; i < nums.length; i++) {
            if (i == 0 || nums[i] != nums[i-1])
                l = res.size();
            k = res.size();
            for (int j = k-l; j < k; j++) {
                temp = new ArrayList<>(res.get(j));
                temp.add(nums[i]);
                res.add(temp);
            }
        }
        return res;
    }