0189-Rotate-Array.py

'''
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?
'''
class Solution:
    def rotate(self, nums: List[int], k: int) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        n = len(nums)
        k %= n
        
        self.reverse(nums, 0, n - 1)
        self.reverse(nums, 0, k - 1)
        self.reverse(nums, k, n - 1)
        
        return nums
        
    def reverse(self, nums, start, end):
        
        while start < end:
            
            nums[start], nums[end] = nums[end], nums[start]
            
            start += 1
            end -= 1