Leetcode题目078-子集

class Solution
{
public:
    vector<vector<int>> subsets(vector<int>& nums)
    {
        vector<vector<int>> res;
        vector<int> path;
        backtrack(nums, res, path, 0 );
        return res;
    }


    void backtrack(vector<int>& nums, vector<vector<int>>& res, vector<int>& path, int start)
{   //回溯算法
        res.push_back(path); //此题全部分支都符合，无需额外的判断条件
        for(int i=start; i < nums.size(); i++)
        {
            path.push_back(nums[i]);//做出选择
            backtrack(nums, res, path, i+1);//递归进入下一层，注意i+1，标识下一个选择列表的开始位置，最重要的一步
            path.pop_back();//撤销选择
        }
    }
};

class Solution {
public:
    vector<int> t;
    vector<vector<int>> ans;


    vector<vector<int>> subsets(vector<int>& nums) {
        int n = nums.size();
        for (int mask = 0; mask < (1 << n); ++mask) {
            t.clear();
            for (int i = 0; i < n; ++i) {
                if (mask & (1 << i)) {
                    t.push_back(nums[i]);
                }
            }
            ans.push_back(t);
        }
        return ans;
    }
};

class Solution:
    def subsets(self, nums: List[int]) -> List[List[int]]:
        res = [[]]
        for i in range(len(nums)):
            path = []
            for r in res:
                path.append(r + [nums[i]])
            res.extend(path)
        return re