Heap Sort Algorithm in Kotlin

In this source code example, we will write a code to implement the Heap Sort algorithm in Kotlin.

Heap sort is a comparison-based sorting technique based on Binary Heap data structure. It is similar to selection sort where we first find the minimum element and place the minimum element at the beginning. We repeat the same process for the remaining elements.

Heap Sort Algorithm in Kotlin

Let's write the Kotlin program to implement the Heap sort algorithm to sort an array of elements in ascending order:
import java.util.*

fun <E: Comparable<E>> Array<E>.sort() {
    val middle = size / 2 - 1
    for (i in middle downTo 0) {
        heapify(this, size, i)
    }
    for (i in size - 1 downTo 0) {
        this[0] = this[i].also { this[i] = this[0] }
        heapify(this, i, 0)
    }
}

private fun <E: Comparable<E>> heapify(arr: Array<E>, heapSize: Int, root: Int) {
    var largest = root
    val leftNode = 2 * root + 1
    val rightNode = 2 * root + 2
    if (leftNode < heapSize && arr[leftNode] > arr[largest]) largest = leftNode
    if (rightNode < heapSize && arr[rightNode] > arr[largest]) largest = rightNode

    if (largest != root) {
        arr[root] = arr[largest].also { arr[largest] = arr[root] }
        heapify(arr, heapSize, largest)
    }
}

fun main(args: Array<String>) {
    val nums = arrayOf(2, 12, 89, 23, 76, 43, 12)
    nums.sort()
    println(Arrays.toString(nums))

    val languages = arrayOf("Kotlin", "Java", "C#", "R", "Python", "Scala", "Groovy", "C", "C++")
    languages.sort()
    println(Arrays.toString(languages))
}

Output:

[2, 12, 12, 23, 43, 76, 89]
[C, C#, C++, Groovy, Java, Kotlin, Python, R, Scala]

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