LeetCode--No.78--Subsets

Given a set of distinct integers, nums, return all possible subsets.

Note: The solution set must not contain duplicate subsets.

For example,
If nums = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

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public class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        res = subsetsHelper(nums);
        return res;
    }
    public List<List<Integer>> subsetsHelper(int[] nums){
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        if (nums.length == 0)
            return res;
        else if (nums.length == 1){
            res.add(new ArrayList<Integer>());
            List<Integer> temp = new ArrayList<Integer>();
            temp.add(nums[0]);
            res.add(temp);
            return res;
        }
        else{
            List<List<Integer>> temp = new ArrayList<List<Integer>>();
            int[] nums_subset = Arrays.copyOfRange(nums, 0, nums.length - 1);
            temp = subsetsHelper(nums_subset);
            int t = nums[nums.length - 1];
            for(List<Integer> list : temp){
                List<Integer> new_list = new ArrayList<Integer>(list);
                new_list.add(t);
                res.add(list);
                res.add(new_list);
            }
            return res;
        }
    }
}

哎哎也是不容易，debug了好久才没语法错误。
需要注意的是：对Temp 这个List<List<Integer>> 进行循环的循环体中，不能对它同时进行修改。

LeetCode--No.78--Subsets

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