LeetCode78 Subsets

题目：

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

Note: The solution set must not contain duplicate subsets. （Medium）

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

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

分析：回溯法或位运算。

回溯的思路就是每个元素可以要可以不要，然后进一步dfs下去。

代码：

 1 class Solution {
 2 private:
 3     void helper(vector<int>& nums, vector<int>& temp, int start, vector<vector<int>>& result) {
 4         if (start == nums.size()) {
 5             return;
 6         }
 7         temp.push_back(nums[start]);
 8         result.push_back(temp);
 9         helper(nums, temp, start + 1, result);
10         temp.pop_back();
11         helper(nums, temp, start + 1, result);
12     }
13 public:
14     vector<vector<int>> subsets(vector<int>& nums) {
15         vector<vector<int>> result;
16         vector<int> temp;
17         result.push_back(temp);
18         helper(nums, temp, 0, result);
19         return result;
20     }
21 };