Merge pull request kodecocodes#887 from abuzeid-ibrahim/master

Insersion sort: rename variables with convenience names

Author: richard-ash

Insertion Sort/InsertionSort.playground/Contents.swift

@@ -9,35 +9,35 @@
 func insertionSort<T>(_ array: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
     guard array.count > 1 else { return array }
 
-    var a = array
-    for x in 1..<a.count {
-        var y = x
-        let temp = a[y]
-        while y > 0 && isOrderedBefore(temp, a[y - 1]) {
-            a[y] = a[y - 1]
-            y -= 1
+    var sortedArray = array
+    for index in 1..<sortedArray.count {
+        var currentIndex = index
+        let temp = sortedArray[currentIndex]
+        while currentIndex > 0 && isOrderedBefore(temp, sortedArray[currentIndex - 1]) {
+            sortedArray[currentIndex] = sortedArray[currentIndex - 1]
+            currentIndex -= 1
         }
-        a[y] = temp
+        sortedArray[currentIndex] = temp
     }
-    return a
+    return sortedArray
 }
 
 /// Performs the Insertion sort algorithm to a given array
 ///
 /// - Parameter array: the array to be sorted, conatining elements that conform to the Comparable protocol
 /// - Returns: a sorted array containing the same elements
 func insertionSort<T: Comparable>(_ array: [T]) -> [T] {
-    var a = array
-    for x in 1..<a.count {
-        var y = x
-        let temp = a[y]
-        while y > 0 && temp < a[y - 1] {
-            a[y] = a[y - 1]
-            y -= 1
+    var sortedArray = array
+    for index in 1..<sortedArray.count {
+        var currentIndex = index
+        let temp = sortedArray[currentIndex]
+        while currentIndex > 0 && temp < sortedArray[currentIndex - 1] {
+            sortedArray[currentIndex] = sortedArray[currentIndex - 1]
+            currentIndex -= 1
         }
-        a[y] = temp
+        sortedArray[currentIndex] = temp
     }
-    return a
+    return sortedArray
 }
 
 let list = [ 10, -1, 3, 9, 2, 27, 8, 5, 1, 3, 0, 26 ]

Insertion Sort/InsertionSort.playground/contents.xcplayground

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

Insertion Sort/InsertionSort.swift

@@ -5,19 +5,19 @@
 ///   - isOrderedBefore: returns true if the elements provided are in the corect order
 /// - Returns: a sorted array containing the same elements
 func insertionSort<T>(_ array: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
-  guard array.count > 1 else { return array }
-
-  var a = array
-  for x in 1..<a.count {
-    var y = x
-    let temp = a[y]
-    while y > 0 && isOrderedBefore(temp, a[y - 1]) {
-      a[y] = a[y - 1]
-      y -= 1
+    guard array.count > 1 else { return array }
+    ///   - sortedArray: copy the array to save stability
+    var sortedArray = array
+    for index in 1..<sortedArray.count {
+        var currentIndex = index
+        let temp = sortedArray[currentIndex]
+        while currentIndex > 0, isOrderedBefore(temp, sortedArray[currentIndex - 1]) {
+            sortedArray[currentIndex] = sortedArray[currentIndex - 1]
+            currentIndex -= 1
+        }
+        sortedArray[currentIndex] = temp
     }
-    a[y] = temp
-  }
-  return a
+    return sortedArray
 }
 
 /// Performs the Insertion sort algorithm to a given array
@@ -27,15 +27,15 @@ func insertionSort<T>(_ array: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
 func insertionSort<T: Comparable>(_ array: [T]) -> [T] {
     guard array.count > 1 else { return array }
 
-    var a = array
-    for x in 1..<a.count {
-        var y = x
-        let temp = a[y]
-        while y > 0 && temp < a[y - 1] {
-            a[y] = a[y - 1]
-            y -= 1
+    var sortedArray = array
+    for index in 1..<sortedArray.count {
+        var currentIndex = index
+        let temp = sortedArray[currentIndex]
+        while currentIndex > 0, temp < sortedArray[currentIndex - 1] {
+            sortedArray[currentIndex] = sortedArray[currentIndex - 1]
+            currentIndex -= 1
         }
-        a[y] = temp
+        sortedArray[currentIndex] = temp
     }
-    return a
+    return sortedArray
 }

Insertion Sort/README.markdown

@@ -91,15 +91,15 @@ Here is an implementation of insertion sort in Swift:
 
 ```swift
 func insertionSort(_ array: [Int]) -> [Int] {
-    var a = array			 // 1
-    for x in 1..<a.count {		 // 2
-        var y = x
-        while y > 0 && a[y] < a[y - 1] { // 3
-            a.swapAt(y - 1, y)
-            y -= 1
+    var sortedArray = array			 // 1
+    for index in 1..<sortedArray.count {		 // 2
+        var currentIndex = index
+        while currentIndex > 0 && sortedArray[currentIndex] < sortedArray[currentIndex - 1] { // 3
+            sortedArray.swapAt(currentIndex - 1, currentIndex)
+            currentIndex -= 1
         }
     }
-    return a
+    return sortedArray
 }
 
 
@@ -154,17 +154,17 @@ In code that looks like this:
 
 ```swift
 func insertionSort(_ array: [Int]) -> [Int] {
-  var a = array
-  for x in 1..<a.count {
-    var y = x
-    let temp = a[y]
-    while y > 0 && temp < a[y - 1] {
-      a[y] = a[y - 1]                // 1
-      y -= 1
+  var sortedArray = array
+  for index in 1..<sortedArray.count {
+    var currentIndex = index
+    let temp = sortedArray[currentIndex]
+    while currentIndex > 0 && temp < sortedArray[currentIndex - 1] {
+      sortedArray[currentIndex] = sortedArray[currentIndex - 1]                // 1
+      currentIndex -= 1
     }
-    a[y] = temp                      // 2
+    sortedArray[currentIndex] = temp                      // 2
   }
-  return a
+  return sortedArray
 }
 ```