Updating Merge Sort to Swift 3

Merge Sort/MergeSort.playground/Contents.swift

@@ -1,14 +1,14 @@
 /* Top-down recursive version */
 
-func mergeSort(array: [Int]) -> [Int] {
+func mergeSort(_ array: [Int]) -> [Int] {
   guard array.count > 1 else { return array }
   let middleIndex = array.count / 2
   let leftArray = mergeSort(Array(array[0..<middleIndex]))
   let rightArray = mergeSort(Array(array[middleIndex..<array.count]))
   return merge(leftPile: leftArray, rightPile: rightArray)
 }
 
-func merge(leftPile leftPile: [Int], rightPile: [Int]) -> [Int] {
+func merge(leftPile: [Int], rightPile: [Int]) -> [Int] {
   var leftIndex = 0
   var rightIndex = 0
   var orderedPile = [Int]()
@@ -48,7 +48,7 @@ let sortedArray = mergeSort(array)
 
 /* Bottom-up iterative version */
 
-func mergeSortBottomUp<T>(a: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
+func mergeSortBottomUp<T>(_ a: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
   let n = a.count
   var z = [a, a]   // the two working arrays
   var d = 0        // z[d] is used for reading, z[1 - d] for writing

Merge Sort/MergeSort.swift

@@ -6,15 +6,15 @@
 //
 //
 
-func mergeSort(array: [Int]) -> [Int] {
+func mergeSort(_ array: [Int]) -> [Int] {
   guard array.count > 1 else { return array }
   let middleIndex = array.count / 2
   let leftArray = mergeSort(Array(array[0..<middleIndex]))
   let rightArray = mergeSort(Array(array[middleIndex..<array.count]))
   return merge(leftPile: leftArray, rightPile: rightArray)
 }
 
-func merge(leftPile leftPile: [Int], rightPile: [Int]) -> [Int] {
+func merge(leftPile: [Int], rightPile: [Int]) -> [Int] {
   var leftIndex = 0
   var rightIndex = 0
   var orderedPile = [Int]()
@@ -59,7 +59,7 @@ func merge(leftPile leftPile: [Int], rightPile: [Int]) -> [Int] {
   To avoid allocating many temporary array objects, it uses double-buffering with
   just two arrays.
 */
-func mergeSortBottomUp<T>(a: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
+func mergeSortBottomUp<T>(_ a: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
   let n = a.count
   var z = [a, a]   // the two working arrays
   var d = 0        // z[d] is used for reading, z[1 - d] for writing

Merge Sort/README.markdown

@@ -42,7 +42,7 @@ You're left with only two piles and `[9]` finally gets its chance to merge, resu
 Here's what merge sort may look like in Swift:
 
 ```swift
-func mergeSort(array: [Int]) -> [Int] {
+func mergeSort(_ array: [Int]) -> [Int] {
   guard array.count > 1 else { return array }    // 1
 
   let middleIndex = array.count / 2              // 2
@@ -70,7 +70,7 @@ A step-by-step explanation of how the code works:
 Here's the merging algorithm:
 
 ```swift
-func merge(leftPile leftPile: [Int], rightPile: [Int]) -> [Int] {
+func merge(leftPile: [Int], rightPile: [Int]) -> [Int] {
   // 1
   var leftIndex = 0
   var rightIndex = 0
@@ -162,7 +162,7 @@ The implementation of merge sort you've seen so far is called "top-down" because
 Time to step up the game a little. :-) Here is a complete bottom-up implementation in Swift:
 
 ```swift
-func mergeSortBottomUp<T>(a: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
+func mergeSortBottomUp<T>(_ a: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
   let n = a.count
 
   var z = [a, a]      // 1