Understanding How Bubble Sort Works

In this lesson you will learn how to implement bubble sort in Kotlin, so you understand sorting from the ground up. This is for anyone searching for "Kotlin bubble sort implementation".

Bubble sort is a simple algorithm that repeatedly compares two neighbouring values and swaps them if they are in the wrong order. The name comes from the way larger bubbles gradually rise to the surface.

The sample code uses an IntArray and nested for loops, comparing the neighbouring elements arr[j] and arr[j + 1] and swapping them through the temporary variable tmp when they are out of order. Notice the 0 until n - 1 range notation.

A common stumbling block for beginners is the swap itself. You have to park one value in a temporary variable first, and forgetting that loses the original value.

In practice you would use an optimised method such as Kotlin's .sorted(), but this remains an important algorithm for understanding what happens internally.

📖 Reference code

fun bubbleSort(arr: IntArray): IntArray {
    val n = arr.size
    for (i in 0 until n - 1) {
        for (j in 0 until n - 1 - i) {
            if (arr[j] > arr[j + 1]) {
                val tmp = arr[j]
                arr[j] = arr[j + 1]
                arr[j + 1] = tmp
            }
        }
    }
    return arr
}

fun main() {
    val nums = intArrayOf(5, 2, 8, 1, 9)
    println(bubbleSort(nums).joinToString(", "))
}

✍️ Your code

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