19.2.15 [LeetCode 78] Subsets

Given a set of distinct integers, nums, return all possible subsets (the power set).

Note: The solution set must not contain duplicate subsets.

Example:

Input: nums = [1,2,3]
Output:
[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

class Solution {
public:
    void build(vector<vector<int>>&ans, vector<int>&now, vector<int>&nums, int i) {
        for (; i < nums.size(); i++) {
            now.push_back(nums[i]);
            ans.push_back(now);
            build(ans, now, nums, i + 1);
            now.pop_back();
        }
    }
    vector<vector<int>> subsets(vector<int>& nums) {
        vector<vector<int>>ans;
        vector<int>now;
        ans.push_back(vector<int>());
        build(ans, now, nums, 0);
        return ans;
    }
};

好像不太对啊……今天所有的memory usage好像都beat了100%……