Subsets

Given a set of distinct integers, nums, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

 

For example,
If nums = [1,2,3], a solution is:

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

 

Analyse: Each number has two states: selected or not selected. Recursively invoke the choose function until the step equals to the size. Then construct a vector to store all selected numbers, and push it to the result vector.

Runtime: 8ms.

 1 class Solution {
 2 public:
 3     vector<vector<int>> subsets(vector<int>& nums) {
 4         vector<vector<int> > result;
 5         sort(nums.begin(), nums.end());
 6         vector<bool> selected(nums.size(), false);
 7         subset(nums, selected, 0, result);
 8         
 9         return result;
10     }
11     
12     void subset(vector<int> &nums, vector<bool> &selected, int step, vector<vector<int> > &result){
13         if(step == nums.size()){
14             vector<int> temp;
15             for(int i = 0; i < step; i++){
16                 if(selected[i]) temp.push_back(nums[i]);
17             }
18             result.push_back(temp);
19             return;
20         }
21         
22         //not choose the number
23         selected[step] = false;
24         subset(nums, selected, step + 1, result);
25         //choose the number
26         selected[step] = true;
27         subset(nums, selected, step + 1, result);
28     }
29 };