class Solution:
def combine(self, n: int, k: int) -> List[List[int]]:
res = []
# i记录当前有哪些数字已经遍历过
def help(tmp,i):
if len(tmp)==k:
res.append(tmp)
return
for j in range(i, n+1):
help(tmp+[j],j+1)
help([],1)
return res