Subsets <leetcode>

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],
  []
]

算法:该题的解空间类似一个排列树，但是又不完全相同，树种根到所有节点的路径是一个解，还有不要忘了空集。直接用深度优先遍历解决：

10/10test cases passed
Runtime::44ms

class Solution {
public:
    vector<vector<int> > subsets(vector<int> &S) {
       vector<vector<int>> result;
       int len=S.size();
       if(S.size()<=0)  return result;
        sort(S.begin(),S.end());
        vector<int>  temp;
        doit(result,S,0,len,temp);
        return result;
    }
    void doit(vector<vector<int>> &result,vector<int> &s,int dep,int len,vector<int> &temp)
    {
        result.push_back(temp);
        for(int i=dep;i<len;i++)
        {
            temp.push_back(s[i]);
            doit(result,s,i+1,len,temp);
            temp.pop_back();
        }
    }
};