reduceRightIndexed

Accumulates value starting with the last character and applying operation from right to left to each character with its index in the original char sequence and current accumulator value.

Throws an exception if this char sequence is empty. If the char sequence can be empty in an expected way, please use reduceRightIndexedOrNull instead. It returns null when its receiver is empty.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.reduceRight { string, acc -> acc + string }) // dcba
println(strings.reduceRightIndexed { index, string, acc -> acc + string + index }) // dc2b1a0

// emptyList<Int>().reduceRight { _, _ -> 0 } //  will fail
//sampleEnd
}

Parameters

operation - function that takes the index of a character, the character itself and current accumulator value, and calculates the next accumulator value.