Given a set of distinct integers, S, 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 S = [1,2,3], a solution is:

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

  class Solution {
  public:
      std::vector
      
        > subsets(std::vector
       
         &S) { std::sort(S.begin(),S.end()); dfs(std::vector
        
         (),S,0); return result; } private: std::vector
         
          > result; void dfs(std::vector
          
            vec, std::vector
           
             &S, int n) { if(n == S.size()) { result.push_back(vec); return; } else { dfs(vec,S,n+1); vec.push_back(S[n]); dfs(vec,S,n+1); } } };