189. Rotate Array

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

Example 1:

• Input: nums = [1,2,3,4,5,6,7], 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: nums = [-1,-100,3,99], 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]

Constraints:

• 1 <= nums.length <= 10^5
• -2^31 <= nums[i] <= 2^31 - 1
• 0 <= k <= 10^5
• Try to come up with as many solutions as you can. There are at least three different ways to solve this problem.
• Could you do it in-place with O(1) extra space?

Solution

class Solution:
    def rotate(self, nums: list[int], k: int) -> None:
        N = len(nums) - 1
        cut = k % len(nums)

        def reverse(l, r):
            while l <= r:
                nums[l], nums[r] = nums[r], nums[l]
                l += 1
                r -= 1

        reverse(0, N)
        reverse(0, cut - 1)
        reverse(cut, N)