189. Rotate Array

Given an array, rotate the array to the right by k steps, where k is non-negative.

Follow up:

• Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.
• Could you do it in-place with O(1) extra space?

给出一个数组和k，让你把数组往右移动k部，超出数组的部分移动到数组的头部，实际上有很多种解法。

如果要求O1的额外空间的话，做法就有点有意思了。

可以两段先反转，然后再整体反转，举个例子，[1,2,3,4,5,6,7] k= 3 -> [4,3,2,1] [7,6,5] ->[5,6,7,1,2,3,4]

神奇吧

class Solution(object):
    def rotate(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: None Do not return anything, modify nums in-place instead.
        """
        n = len(nums)
        k = k % n
        for i in range(0, (n - k + 1) // 2, 1):
            nums[i],  nums[n - k - i - 1] = nums[n - k - i - 1], nums[i]
        for i in range(0, (k + 1) // 2, 1):
            nums[n - k + i], nums[n - i - 1] = nums[n - i - 1], nums[n - k + i]
        for i in range(0, n // 2, 1):
            nums[i], nums[n - i - 1] = nums[n - i - 1], nums[i]
        

 

[1,2,3,4,5,6,7], k = 3