Permutations: Difference between revisions

</pre>

=== Using rotate ===

<syntaxhighlight lang="kotlin">

fun <T> List<T>.rotateLeft(n: Int) = drop(n) + take(n)

fun <T> permute(input: List<T>): List<List<T>> =

when (input.isEmpty()) {

true -> listOf(input)

else -> {

permute(input.drop(1))

.map { it + input.first() }

.flatMap { subPerm -> List(subPerm.size) { i -> subPerm.rotateLeft(i) } }

}

}

fun main(args: Array<String>) {

permute(listOf(1, 2, 3)).also {

println("""There are ${it.size} permutations:

|${it.joinToString(separator = "\n")}""".trimMargin())

}

}

</syntaxhighlight>

{{out}}

<pre>

There are 6 permutations:

[3, 2, 1]

[2, 1, 3]

[1, 3, 2]

[2, 3, 1]

[3, 1, 2]

[1, 2, 3]