Description

Submission

class Solution {
public:
    vector<vector<int>> subsets(vector<int>& nums) {
        vector<int> curr;
        vector<vector<int>> res;
        powerset(nums, curr, nums.size() - 1, res);
        return res;
    }
private:
    void powerset(vector<int>& nums, vector<int> curr, int index, vector<vector<int>>& res) {
        if(index == 0) {
            res.push_back(curr);
            curr.push_back(nums[0]);
            res.push_back(curr);
            return;
        }
        powerset(nums, curr, index - 1, res);
        curr.push_back(nums[index]);
        powerset(nums, curr, index - 1, res);
    }
};

Submission 200912

class Solution {
public:
    vector<vector<int>> subsets(vector<int>& nums) {
        vector<vector<int>> res;
        vector<int> hand;
        backtrack(nums, res, hand, 0);
        return res;
    }
private:
    void backtrack(vector<int>& nums, vector<vector<int>>& res, vector<int>& hand, int k) {
        if(k == nums.size()) {
            res.push_back(hand);
            return;
        }
        
        // without the number
        backtrack(nums, res, hand, k+1);
        hand.push_back(nums[k]);
        
        // with the number
        backtrack(nums, res, hand, k+1);
        
        // back to original state
        hand.pop_back();
    }
};