216. 组合总和 III

class Solution {
public:
    vectorint> >ans;
    vector<int>path;
    void backtracking(int n,int k,int sum,int star){
        if(path.size()==k){
            if(sum==n)ans.push_back(path);
            return;
        }
        for(int i=star;i<=9;i++){
            sum+=i;
            path.push_back(i);
            backtracking(n,k,sum,i+1);
            sum-=i;
            path.pop_back();
        }
    }
    vectorint>> combinationSum3(int k, int n) {
        backtracking(n,k,0,1);
        return ans;
    }
};