September 2017 Update

Task/Sorting-algorithms-Permutation-sort/Kotlin/sorting-algorithms-permutation-sort.kotlin

@@ -0,0 +1,49 @@
+// version 1.1.2
+
+fun <T : Comparable<T>> isSorted(list: List<T>): Boolean {
+    val size = list.size
+    if (size < 2) return true
+    for (i in 1 until size) {
+        if (list[i] < list[i - 1]) return false
+    }
+    return true
+}
+
+fun <T : Comparable<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 <T : Comparable<T>> permutationSort(input: List<T>): List<T> {
+    if (input.size == 1) return input
+    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)
+            if (isSorted(newPerm)) return newPerm
+        }
+    }
+    return input
+}
+
+fun main(args: Array<String>) {
+    val input = listOf('d', 'b', 'e', 'a', 'f', 'c')
+    println("Before sorting : $input")
+    val output = permutationSort(input)
+    println("After sorting  : $output")
+    println()
+    val input2 = listOf("first", "second", "third", "fourth", "fifth", "sixth")
+    println("Before sorting : $input2")
+    val output2 = permutationSort(input2)
+    println("After sorting  : $output2")
+}