Swap two elements of a List in Kotlin

This article explores different ways to swap two elements of a list in Kotlin.

1. Using `Collections.swap()` function

The Collections.swap() function swaps the elements at the specified positions in the specified list. It can be used as follows:

import java.util.*

fun main() {

val nums = listOf(1, 2, 3, 4, 5)

Collections.swap(nums, 1, 3)

println(nums)

}

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Output:

[1, 4, 3, 2, 5]

If your input is an array, you can use the Collections.swap() function to swap two elements in it. Since the Collections.swap() function accepts a list, you can get a fixed-size list “backed” by the array. Now any changes made to the backed list are reflected in the array as well.

import java.util.*

fun main() {

val nums = arrayOf(1, 2, 3, 4, 5)

Collections.swap(nums.asList(), 1, 3)

println(nums.contentToString())

}

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Output:

[1, 4, 3, 2, 5]

2. Using Custom Logic

You can write your utility function for swapping two elements in a list. This can be implemented as follows:

fun <T> swap(list: MutableList<T>, i: Int, j: Int) {

val t = list[i]

list[i] = list[j]

list[j] = t

}

fun main() {

val nums = mutableListOf(1, 2, 3, 4, 5)

swap(nums, 1, 3)

println(nums)

}

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Output:

[1, 4, 3, 2, 5]

Here’s an equivalent way to do it for arrays:

fun <T> swap(arr: Array<T>, i: Int, j: Int) {

val t = arr[i]

arr[i] = arr[j]

arr[j] = t

}

fun main() {

val nums = arrayOf(1, 2, 3, 4, 5)

swap(nums, 1, 3)

println(nums.contentToString())

}

Download Code

Output:

[1, 4, 3, 2, 5]

That’s all about swapping two elements of a list in Kotlin.

Swap two elements of a List in Kotlin

1. Using Collections.swap() function

2. Using Custom Logic

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1. Using `Collections.swap()` function