Leetcode 78. 子集

参考Leetcode 77. 组合，相当于求nums[0…n-1],子集个数为0～n的所有集合

class Solution {
public:
    vector<vector<int>> ans;
    vector<int> tmp;
    void dfs(int cnt, vector<int>& nums, int index) {
        if (!cnt) {
            ans.push_back(tmp); return;
        }
        for (int i = index; i + cnt - 1 < nums.size(); ++i)
            tmp.push_back(nums[i]), dfs(cnt - 1, nums, i + 1), tmp.pop_back();
    }
    vector<vector<int>> subsets(vector<int>& nums) {
        for (int k = 0; k <= nums.size(); ++k)
            dfs(k, nums, 0);
        return ans;
    }
};