题目：
题解：
class Solution:
def combine(self, n: int, k: int) -> List[List[int]]:
ans = []
path = []
def dfs(x):
remain = k - len(path)
if not remain:
ans.append(list(path))
return
if n + 1 - x > remain:
dfs(x + 1)
path.append(x)
dfs(x + 1)
path.pop()
dfs(1)
return ans
