subsets

[
[3],
[1],
[2],
[1,2,3],
[1,3],
[2,3],
[1,2],
[]
]

class Solution {
public:
/**
* @param S: A set of numbers.
* @return: A list of lists. All valid subsets.
*/
vector<vector<int> > subsets(vector<int> &nums) {
// write your code here
vector<vector<int>> res=vector<vector<int>>(1,vector<int>());
for(int i=0;i<nums.size();i++){
int n=res.size();
for(int j=0;j<n;j++){
res.push_back(res[j]);
res.back().push_back(nums[i]);
}
}
return res;
}
};