[Swift 4] Update Shell Sort

Shell Sort/README.markdown

@@ -117,24 +117,10 @@ Here is an implementation of Shell Sort in Swift:
 var arr = [64, 20, 50, 33, 72, 10, 23, -1, 4, 5]
 
 public func shellSort(_ list: inout [Int]) {
-
     var sublistCount = list.count / 2
-
     while sublistCount > 0 {
-
-        for index in 0..<list.count {
-
-            guard index + sublistCount < list.count else { break }
-
-            if list[index] > list[index + sublistCount] {
-                swap(&list[index], &list[index + sublistCount])
-            }
-
-            guard sublistCount == 1 && index > 0 else { continue }
-
-            if list[index - 1] > list[index] {
-                swap(&list[index - 1], &list[index])
-            }
+        for pos in 0..<sublistCount {
+            insertionSort(&list, start: pos, gap: sublistCount)
         }
         sublistCount = sublistCount / 2
     }

Shell Sort/Shell Sort.playground/Contents.swift

@@ -0,0 +1,34 @@
+//: Playground - noun: a place where people can play
+
+import UIKit
+
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+    print("Hello, Swift 4!")
+#endif
+
+public func insertionSort(_ list: inout [Int], start: Int, gap: Int) {
+    for i in stride(from: (start + gap), to: list.count, by: gap) {
+        let currentValue = list[i]
+        var pos = i
+        while pos >= gap && list[pos - gap] > currentValue {
+            list[pos] = list[pos - gap]
+            pos -= gap
+        }
+        list[pos] = currentValue
+    }
+}
+
+public func shellSort(_ list: inout [Int]) {
+    var sublistCount = list.count / 2
+    while sublistCount > 0 {
+        for pos in 0..<sublistCount {
+            insertionSort(&list, start: pos, gap: sublistCount)
+        }
+        sublistCount = sublistCount / 2
+    }
+}
+
+var arr = [64, 20, 50, 33, 72, 10, 23, -1, 4, 5]
+
+shellSort(&arr)

Shell Sort/Shell Sort.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>