Problem Solving

4. Rotate Array by K Steps

Problem Statement

Given an array of integers and a number k, rotate the array to the right by k steps. After rotation, each element should shift to its new position, and elements that move past the end should wrap around to the beginning.

Solution (Kotlin)

fun main() {
    val arr = arrayOf(12, 35, 1, 10, 34, 1)
    val kInput = 3

    val n = arr.size
    val k = kInput % n  // handle cases where k > n

    if (k == 0) {
        println(arr.joinToString())
        return
    }

    val rotated = arrayListOf()

    // Add last k elements
    for (i in n - k until n) {
        rotated.add(arr[i])
    }

    // Add remaining elements
    for (i in 0 until n - k) {
        rotated.add(arr[i])
    }

    println(rotated.joinToString())
}
    

Explanation

To rotate the array by k steps, we logically split the array into two parts:

• Part 1: The last k elements, which will move to the front
• Part 2: The first n - k elements, which will follow after

By taking the last k elements first and then appending the remaining elements, we construct the rotated array in O(n) time. The operation k % n ensures the rotation works even if k is larger than the array size (e.g., rotating 10 steps in a size-6 array is same as rotating 4 steps). The final rotated array is printed as output.