Given a set of distinct integers, nums, return all possible subsets (the power set).

Note: 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],  []]

利用回溯法求出给定数组的所有不重复子数组。

这个题没有边界条件，所以使用直接使用回溯标准形式即可

class Solution {public:    vector
     
      
       > subsets(vector
       
        & nums) {        vector
        
         
          > res;        vector
          
            tmp; int idx = 0; helper(res, tmp, nums, idx); return res; } void helper(vector
           
            
             >& res, vector
             
              & tmp, vector
              
               & nums, int idx) { res.push_back(tmp); for (int i = idx; i < nums.size(); i++) { tmp.push_back(nums[i]); helper(res, tmp, nums, i + 1); tmp.pop_back(); } }};// 6 ms