# Question

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

Example 1:

Input: [1,2,3,4,5,6,7] and k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]


Example 2:

Input: [-1,-100,3,99] and k = 2
Output: [3,99,-1,-100]
Explanation:
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]


Note:

• 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?

# Solution

The solution can be obtained by reversing the entire array, then reversing the first k elements, and reversing the last n-k elements.

class Solution(object):
def rotate(self, nums, k):
"""
:type nums: List[int]
:type k: int
:rtype: void Do not return anything, modify nums in-place instead.
"""
length = len(nums)
if length <= 1 or k == 0 or k % length == 0:
return

nums.reverse()
if k > length:
k = k % length

left, right = 0, k - 1
while right > left:
nums[left], nums[right] = nums[right], nums[left]
left += 1
right -= 1

left, right = k, length - 1
while right > left:
nums[left], nums[right] = nums[right], nums[left]
left += 1
right -= 1