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LeetCode 189 Rotate Array - Medium

189. Rotate Array -- Medium

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189. Rotate Array — Medium

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Problem

  1. Rotate Array -- Medium

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?

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 <= 2 * 104 -231 <= nums[i] <= 231 - 1 0 <= k <= 105

Solution

class Solution:
    def reverse(self, nums: list, start: int, end: int) -> None:
        while start < end:
            nums[start], nums[end] = nums[end], nums[start]
            start, end = start + 1, end - 1
                
    def rotate(self, nums: List[int], k: int) -> None:
        n = len(nums)
        k %= n #because k might be quite large, so mod with n to get equivalent steps
        self.reverse(nums, 0, n - 1)
        self.reverse(nums, 0, k - 1)
        self.reverse(nums, k, n - 1)

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