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189. Rotate Array

Medium

Given an array, 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 <= 105
• -231 <= nums[i] <= 231 - 1
• 0 <= k <= 105

Follow up:

• 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

object Solution {
    private def reverse(nums: Array[Int], l: Int, r: Int): Unit = {
        var left = l
        var right = r
        while (left <= right) {
            val temp = nums(left)
            nums(left) = nums(right)
            nums(right) = temp
            left += 1
            right -= 1
        }
    }

    def rotate(nums: Array[Int], k: Int): Unit = {
        val n = nums.length
        val t = n - (k % n)
        reverse(nums, 0, t - 1)
        reverse(nums, t, n - 1)
        reverse(nums, 0, n - 1)
    }
}

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