78. Subsets

1.問題

• 給一組不重複整數, 回傳所有的子集合

2.想法

• Recursive + back tracking

3.程式碼

class Solution {
public:
    vector<vector<int>> subsets(vector<int>& nums) {
        vector<vector<int>> subsets;
        vector<int> record;
        for (int i = 0; i < nums.size(); i++) {
            getSubSet(subsets, record, nums, 0, i + 1);
        }
        subsets.push_back(vector<int>());
        return subsets;
    }
private:
    void getSubSet(vector<vector<int>>& subsets, vector<int>& record, vector<int>& nums, int start, int numMember){
        if (numMember == record.size()) {
            subsets.push_back(record);
            return;
        }
        for (int i = start; i < nums.size(); i++) {
            record.push_back(nums[i]);
            getSubSet(subsets, record, nums, i + 1, numMember);
            record.pop_back();
        }
    }
};

4.Performance