LeetCode 78. 子集

给定一组不含重复元素的整数数组 nums，返回该数组所有可能的子集（幂集）。

说明：解集不能包含重复的子集。

示例:

输入: nums = [1,2,3]
输出:
[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

class Solution {
public:
    int n;
    vector<vector<int>> ans;
    vector<int> v;
    vector<vector<int>> subsets(vector<int>& nums) {
        n = nums.size();
        if(n == 0)
        {
            ans.push_back(v);
        }
        else
            dfs(0,nums);
        return ans;
    }
    void dfs(int x,vector<int>& nums)
    {
        if(x == n)
        {
            ans.push_back(v);
            return ;
        }
        ans.push_back(v);
        for(int i = x;i < n;i++)
        {
            v.push_back(nums[i]);
            dfs(i + 1,nums);
            v.pop_back();
        }
    }
};

class Solution {
public:
    vector<vector<int>> subsets(vector<int>& nums) {
    vector<vector<int>> res;
    res.push_back({});
    if(nums.size()==0) return res;
    for(auto i:nums)
    {
        int k=res.size();
        vector<vector<int>> tmp(res);
        for(int j=0;j<k;j++)
        {
            tmp[j].push_back(i);
            res.push_back(tmp[j]);
        }
        
    }
    return res;
    }
};

class Solution {
public:
    vector<vector<int>> subsets(vector<int>& nums) {
        vector<vector<int>> ret;
        ret.push_back({});
        int size=nums.size();
        int subsize=pow(2,size);
        int hash=1;
        while(hash<subsize){
            vector<int> temp;
            for(int k=0;k<size;k++) {
                int a=1<<k;
                if(a&hash) {
                    temp.push_back(nums[k]);
                }
            }
            ret.push_back(temp);
            hash++;
        }
        return ret;
    }
};