Bubble Sort in Kotlin: A Comprehensive Guide

By Syed Wahaj

Introduction

Sorting is a fundamental operation in computer science, and various algorithms have been developed to efficiently organize data. One such elementary sorting algorithm is Bubble Sort. In this article, we will explore Bubble Sort and implement it using the Kotlin programming language.

Understanding Bubble Sort

Bubble Sort is a simple comparison-based sorting algorithm that repeatedly steps through the list, compares adjacent elements, and swaps them if they are in the wrong order. The pass through the list is repeated until the list is sorted.

The algorithm gets its name because smaller elements “bubble” to the top of the list, while larger elements “sink” to the bottom. Despite its simplicity, Bubble Sort is not the most efficient algorithm for large datasets, as its average and worst-case time complexity is O(n^2).

Kotlin Implementation

Let’s dive into a Kotlin implementation of Bubble Sort. We will create a function called bubbleSort that takes an array of comparable elements as an argument and sorts it in ascending order.

fun <T : Comparable<T>> bubbleSort(arr: Array<T>) {
    val n = arr.size

    for (i in 0 until n - 1) {
        for (j in 0 until n - i - 1) {
            if (arr[j] > arr[j + 1]) {
                // Swap arr[j] and arr[j+1]
                val temp = arr[j]
                arr[j] = arr[j + 1]
                arr[j + 1] = temp
            }
        }
    }
}

Here, the function takes an array of comparable elements (T) and uses nested loops to iterate through the array, comparing adjacent elements and swapping them if they are out of order. The inner loop ensures that the largest unsorted element “bubbles” to its correct position in each pass.

Example Usage

Now, let’s demonstrate how to use the bubbleSort function with a simple example:

fun main() {
    val unsortedArray = arrayOf(64, 34, 25, 12, 22, 11, 90)

    println("Unsorted Array: ${unsortedArray.joinToString()}")

    bubbleSort(unsortedArray)

    println("Sorted Array: ${unsortedArray.joinToString()}")
}

In this example, we create an array of integers, print the unsorted array, apply the bubbleSort function, and then print the sorted array.

Optimizing Bubble Sort

While Bubble Sort is straightforward, it may not be the most efficient choice for sorting large datasets. However, we can make some optimizations to the basic algorithm to improve its performance in certain cases.

Early Exit

One optimization involves introducing a flag to check whether any swaps occurred during a pass. If no swaps occurred, it means the array is already sorted, and we can exit early.

Let’s modify the bubbleSort function to include this optimization:

fun <T : Comparable<T>> bubbleSortOptimized(arr: Array<T>) {
    val n = arr.size
    var swapped: Boolean

    for (i in 0 until n - 1) {
        swapped = false
        for (j in 0 until n - i - 1) {
            if (arr[j] > arr[j + 1]) {
                // Swap arr[j] and arr[j+1]
                val temp = arr[j]
                arr[j] = arr[j + 1]
                arr[j + 1] = temp
                swapped = true
            }
        }

        // If no two elements were swapped by inner loop, the array is already sorted
        if (!swapped) break
    }
}

This modification introduces the swapped variable, which is used to check if any swaps occurred during a pass. If no swaps occurred, the function breaks out of the outer loop, as the array is already sorted.

Example Usage with Optimized Bubble Sort

Let’s use the optimized version of Bubble Sort in a similar example:

fun main() {
    val unsortedArray = arrayOf(64, 34, 25, 12, 22, 11, 90)

    println("Unsorted Array: ${unsortedArray.joinToString()}")

    bubbleSortOptimized(unsortedArray)

    println("Sorted Array: ${unsortedArray.joinToString()}")
}