Data commit

Task/Permutations/Kotlin/permutations-1.kotlin

@@ -0,0 +1,22 @@
+// version 1.1.2
+
+fun <T> permute(input: List<T>): List<List<T>> {
+    if (input.size == 1) return listOf(input)
+    val perms = mutableListOf<List<T>>()
+    val toInsert = input[0]
+    for (perm in permute(input.drop(1))) {
+        for (i in 0..perm.size) {
+            val newPerm = perm.toMutableList()
+            newPerm.add(i, toInsert)
+            perms.add(newPerm)
+        }
+    }
+    return perms
+}
+
+fun main(args: Array<String>) {
+    val input = listOf('a', 'b', 'c', 'd')
+    val perms = permute(input)
+    println("There are ${perms.size} permutations of $input, namely:\n")
+    for (perm in perms) println(perm)
+}

Task/Permutations/Kotlin/permutations-2.kotlin

@@ -0,0 +1,18 @@
+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())
+    }
+}