216. Combination Sum III

class Solution {private:    void search(vector<vector<int>> &ret,vector<int> &cur,int start,int k,int target)    {        if(cur.size()>=k)            return;        for(int i=start;i<=9;i++)        {            if(cur.size()==k-1&&i==target)            {                cur.push_back(i);                ret.push_back(cur);                cur.pop_back();            }            else            {                cur.push_back(i);                search(ret,cur,i+1,k,target-i);                cur.pop_back();            }        }    }public:    vector<vector<int>> combinationSum3(int k, int n) {        vector<vector<int>> ret;        vector<int>temp;        search(ret,temp,1,k,n);        return ret;    }};