1. 209

minimum-size-subarray-sum

2. 算法

http://www.cnblogs.com/grandyang/p/4537983.html

• 回溯dfs:O(n!)

3. 代码

class  Solution{
public:
    vector<vector<int> >  combinationSum3(int k,int n){
        vector<vector<int> > res;
        vector<int> out;
        combinationSum3(k,n,1,out,res);
        return res;
    }
private:
    void combinationSum3(int k,int n,int level,vector<int>& out,vector<vector<int> >& res){
        if(n<0)  return;
        if(n==0 && out.size()==k)  res.push_back(out);
        for(int i=level;i<=9;i++){
            out.push_back(i);
            combinationSum3(k,n-i,i+1,out,res);
            out.pop_back();
        }
    }
};