```
def combinationSum3(self, k, n):
self.solution = []
self.helper(1, k, n, [])
return self.solution
def helper(self,start, k, n, result):
if k == 0 and n == 0:
self.solution.append(result[:])
for num in range(start, 10):
result.append(num)
if n-num >= 0:
self.helper(num+1, k - 1, n-num, result)
result.pop()
```