class Solution:

    def combinationSum3(self, k: int, n: int) -> List[List[int]]:

        res = []

        def helper(k,n,start,tmp):

            if k==0:

                if n==0:

                    res.append(tmp)

                return

            for i in range(start,10):

                if n - i < 0:break

                helper(k-1,n-i,i+1,tmp+[i])

        helper(k,n,1,[])

        return res