189. 轮转数组
class Solution:
def rotate(self, nums: List[int], k: int) -> None:
"""
Do not return anything, modify nums in-place instead.
"""
# 如果用nums= 会在新对象上操作。要用[:]给每个元素拷贝
nums[:] = nums[-(k % len(nums)):] + nums[:-(k % len(nums))]