Prepend an element to a list in Kotlin

This article explores different ways to prepend an element to a list in Kotlin. In other words, insert an element at the front of the list.

1. Using `add()` function

The standard solution to prepend an element to the front of a list, you can use the add() function with the specified index as 0.

fun <T> MutableList<T>.prepend(element: T) {

add(0, element)

}

fun main() {

var list = mutableListOf(2, 3, 4, 5)

list.prepend(1)

println(list) // [1, 2, 3, 4, 5]

}

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You can easily extend the solution to add multiple elements to the front of the list.

fun <T> MutableList<T>.prependAll(elements: List<T>) {

addAll(0, elements)

}

fun main() {

var list = mutableListOf(3, 4, 5)

list.prependAll(listOf(1, 2))

println(list) // [1, 2, 3, 4, 5]

}

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2. Using `LinkedList`‘s `push()` function

If you’re using Doubly linked list implementation of the List and Deque interfaces, say a LinkedList, you can easily prepend elements to it with native push() function. This is demonstrated below:

import java.util.LinkedList

fun main() {

val list = LinkedList(listOf(2, 3, 4, 5))

list.push(1)

println(list) // [1, 2, 3, 4, 5]

}

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This function is equivalent to the addFirst() function.

import java.util.LinkedList

fun main() {

val list = LinkedList(listOf(2, 3, 4, 5))

list.addFirst(1)

println(list) // [1, 2, 3, 4, 5]

}

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3. Using `+` operator

Another solution is to wrap the given element in a list and then use the + operator to concatenate the new list with the original list.

fun main() {

var list = listOf(2, 3, 4, 5)

list = listOf(1) + list

println(list) // [1, 2, 3, 4, 5]

}

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The + operator is equivalent to the plus() function shown below:

fun main() {

var list = listOf(2, 3, 4, 5)

list = listOf(1).plus(list)

println(list) // [1, 2, 3, 4, 5]

}

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That’s all about prepending an element to a list in Kotlin.

Prepend an element to a list in Kotlin

1. Using add() function

2. Using LinkedList‘s push() function

3. Using + operator

Share this:

1. Using `add()` function

2. Using `LinkedList`‘s `push()` function

3. Using `+` operator