Add shellsort

DIRECTORY.md

@@ -37,6 +37,7 @@
         * [Mergesort](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/sort/MergeSort.kt)
         * [Quicksort](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/sort/QuickSort.kt)
         * [Selectionsort](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/sort/SelectionSort.kt)
+        * [Shellsort](https://github.com/TheAlgorithms/Kotlin/blob/master/src/main/kotlin/sort/ShellSort.kt)
   * Test
       * Dynamic Programming
         * [Palindromepartitioningtest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/dynamic_programming/PalindromePartitioningTest.kt)
@@ -72,3 +73,4 @@
         * [Mergesorttest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/sort/MergeSortTest.kt)
         * [Quicksorttest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/sort/QuickSortTest.kt)
         * [Selectionsorttest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/sort/SelectionSortTest.kt)
+        * [ShellSsorttest](https://github.com/TheAlgorithms/Kotlin/blob/master/src/test/kotlin/sort/ShellSortTest.kt)

src/main/kotlin/sort/ShellSort.kt

@@ -0,0 +1,30 @@
+package sort
+
+/**
+ * This method implements the Shell Sort
+ *
+ * @param array The array to be sorted
+ * @param gaps The gap sequence to be used. Default is [701, 301, 132, 57, 23, 10, 4, 1] (Marcin Ciura's gap sequence)
+ * Sorts the array by decreasing the gap over which it compares elements after each iteration
+ *
+ * Worst-case performance	O(n^2) (worst known worst case gap sequence)
+ *                          O(n log^2 n) (best known worst case gap sequence)
+ * Best-case performance	O(n log n) (most gap sequences)
+ *                          O(n log^2 n) (best known worst-case gap sequence)
+ * Average performance	    depends on gap sequence
+ * Worst-case space complexity	O(1)
+ **/
+fun <T : Comparable<T>> shellSort(array: Array<T>, gaps: Array<Int> = arrayOf(701, 301, 132, 57, 23, 10, 4, 1)) {
+    for (gap in gaps) {
+        if (gap >= array.size)
+            continue
+
+        for (i in gap until array.size) {
+            for (j in i downTo gap step gap) {
+                if (array[j] < array[j - gap]) {
+                    swapElements(array, j, j - gap)
+                }
+            }
+        }
+    }
+}

src/test/kotlin/sort/ShellSortTest.kt

@@ -0,0 +1,31 @@
+package sort
+
+import org.junit.Assert.assertArrayEquals
+import org.junit.Test
+
+class ShellSortTest {
+
+    @Test
+    fun testShellSort1() {
+        val array = arrayOf(4, 3, 2, 8, 1)
+        shellSort(array)
+
+        assertArrayEquals(array, arrayOf(1, 2, 3, 4, 8))
+    }
+
+    @Test
+    fun testShellSort2() {
+        val array = arrayOf(20, 5, 16, -1, 6)
+        shellSort(array)
+
+        assertArrayEquals(array, arrayOf(-1, 5, 6, 16, 20))
+    }
+
+    @Test
+    fun testShellSort3() {
+        val array = arrayOf("A", "D", "E", "C", "B")
+        shellSort(array)
+
+        assertArrayEquals(array, arrayOf("A", "B", "C", "D", "E"))
+    }
+}