Merge pull request kodecocodes#217 from raywenderlich/Swift3Quicksort

Swift3 migration for QuickSort

Author: kelvinlauKL

Quicksort/Quicksort.playground/Contents.swift

@@ -5,7 +5,7 @@ import Foundation
 
 // *** Simple but inefficient version of quicksort ***
 
-func quicksort<T: Comparable>(a: [T]) -> [T] {
+func quicksort<T: Comparable>(_ a: [T]) -> [T] {
   guard a.count > 1 else { return a }
 
   let pivot = a[a.count/2]
@@ -34,7 +34,7 @@ quicksort(list1)
   partition is [low...p-1]; the right partition is [p+1...high], where p is the
   return value.
 */
-func partitionLomuto<T: Comparable>(inout a: [T], low: Int, high: Int) -> Int {
+func partitionLomuto<T: Comparable>(_ a: inout [T], low: Int, high: Int) -> Int {
   let pivot = a[high]
 
   var i = low
@@ -53,7 +53,7 @@ var list2 = [ 10, 0, 3, 9, 2, 14, 26, 27, 1, 5, 8, -1, 8 ]
 partitionLomuto(&list2, low: 0, high: list2.count - 1)
 list2
 
-func quicksortLomuto<T: Comparable>(inout a: [T], low: Int, high: Int) {
+func quicksortLomuto<T: Comparable>(_ a: inout [T], low: Int, high: Int) {
   if low < high {
     let p = partitionLomuto(&a, low: low, high: high)
     quicksortLomuto(&a, low: low, high: p - 1)
@@ -75,7 +75,7 @@ quicksortLomuto(&list2, low: 0, high: list2.count - 1)
   where p is the return value. The pivot value is placed somewhere inside one
   of the two partitions, but the algorithm doesn't tell you which one or where.
 */
-func partitionHoare<T: Comparable>(inout a: [T], low: Int, high: Int) -> Int {
+func partitionHoare<T: Comparable>(_ a: inout [T], low: Int, high: Int) -> Int {
   let pivot = a[low]
   var i = low - 1
   var j = high + 1
@@ -96,7 +96,7 @@ var list3 = [ 8, 0, 3, 9, 2, 14, 10, 27, 1, 5, 8, -1, 26 ]
 partitionHoare(&list3, low: 0, high: list3.count - 1)
 list3
 
-func quicksortHoare<T: Comparable>(inout a: [T], low: Int, high: Int) {
+func quicksortHoare<T: Comparable>(_ a: inout [T], low: Int, high: Int) {
   if low < high {
     let p = partitionHoare(&a, low: low, high: high)
     quicksortHoare(&a, low: low, high: p)
@@ -111,12 +111,12 @@ quicksortHoare(&list3, low: 0, high: list3.count - 1)
 // *** Randomized sorting ***
 
 /* Returns a random integer in the range min...max, inclusive. */
-public func random(min min: Int, max: Int) -> Int {
+public func random(min: Int, max: Int) -> Int {
   assert(min < max)
   return min + Int(arc4random_uniform(UInt32(max - min + 1)))
 }
 
-func quicksortRandom<T: Comparable>(inout a: [T], low: Int, high: Int) {
+func quicksortRandom<T: Comparable>(_ a: inout [T], low: Int, high: Int) {
   if low < high {
     let pivotIndex = random(min: low, max: high)
     (a[pivotIndex], a[high]) = (a[high], a[pivotIndex])
@@ -139,7 +139,7 @@ list4
   Swift's swap() doesn't like it if the items you're trying to swap refer to
   the same memory location. This little wrapper simply ignores such swaps.
 */
-public func swap<T>(inout a: [T], _ i: Int, _ j: Int) {
+public func swap<T>(_ a: inout [T], _ i: Int, _ j: Int) {
   if i != j {
     swap(&a[i], &a[j])
   }
@@ -149,7 +149,7 @@ public func swap<T>(inout a: [T], _ i: Int, _ j: Int) {
   Dutch national flag partitioning.
   Returns a tuple with the start and end index of the middle area.
 */
-func partitionDutchFlag<T: Comparable>(inout a: [T], low: Int, high: Int, pivotIndex: Int) -> (Int, Int) {
+func partitionDutchFlag<T: Comparable>(_ a: inout [T], low: Int, high: Int, pivotIndex: Int) -> (Int, Int) {
   let pivot = a[pivotIndex]
 
   var smaller = low
@@ -175,7 +175,7 @@ var list5 = [ 10, 0, 3, 9, 2, 14, 8, 27, 1, 5, 8, -1, 26 ]
 partitionDutchFlag(&list5, low: 0, high: list5.count - 1, pivotIndex: 10)
 list5
 
-func quicksortDutchFlag<T: Comparable>(inout a: [T], low: Int, high: Int) {
+func quicksortDutchFlag<T: Comparable>(_ a: inout [T], low: Int, high: Int) {
   if low < high {
     let pivotIndex = random(min: low, max: high)
     let (p, q) = partitionDutchFlag(&a, low: low, high: high, pivotIndex: pivotIndex)

Quicksort/README.markdown

@@ -7,7 +7,7 @@ Quicksort is one of the most famous algorithms in history. It was invented way b
 Here's an implementation in Swift that should be easy to understand:
 
 ```swift
-func quicksort<T: Comparable>(a: [T]) -> [T] {
+func quicksort<T: Comparable>(_ a: [T]) -> [T] {
   guard a.count > 1 else { return a }
 
   let pivot = a[a.count/2]
@@ -131,7 +131,7 @@ In the first example of quicksort I showed you, partitioning was done by calling
 Here's an implementation of Lomuto's partitioning scheme in Swift:
 
 ```swift
-func partitionLomuto<T: Comparable>(inout a: [T], low: Int, high: Int) -> Int {
+func partitionLomuto<T: Comparable>(_ a: inout [T], low: Int, high: Int) -> Int {
   let pivot = a[high]
 
   var i = low
@@ -250,7 +250,7 @@ And we return `i`, the index of the pivot element.
 Let's use this partitioning scheme to build quicksort. Here's the code:
 
 ```swift
-func quicksortLomuto<T: Comparable>(inout a: [T], low: Int, high: Int) {
+func quicksortLomuto<T: Comparable>(_ a: inout [T], low: Int, high: Int) {
   if low < high {
     let p = partitionLomuto(&a, low: low, high: high)
     quicksortLomuto(&a, low: low, high: p - 1)
@@ -277,7 +277,7 @@ This partitioning scheme is by Hoare, the inventor of quicksort.
 Here is the code:
 
 ```Swift
-func partitionHoare<T: Comparable>(inout a: [T], low: Int, high: Int) -> Int {
+func partitionHoare<T: Comparable>(_ a: inout [T], low: Int, high: Int) -> Int {
   let pivot = a[low]
   var i = low - 1
   var j = high + 1
@@ -318,7 +318,7 @@ The pivot is placed somewhere inside one of the two partitions, but the algorith
 Because of these differences, the implementation of Hoare's quicksort is slightly different:
 
 ```swift
-func quicksortHoare<T: Comparable>(inout a: [T], low: Int, high: Int) {
+func quicksortHoare<T: Comparable>(_ a: inout [T], low: Int, high: Int) {
   if low < high {
     let p = partitionHoare(&a, low: low, high: high)
     quicksortHoare(&a, low: low, high: p)
@@ -380,7 +380,7 @@ Another common solution is to choose the pivot randomly. Sometimes this may resu
 Here is how you can do quicksort with a randomly chosen pivot:
 
 ```swift
-func quicksortRandom<T: Comparable>(inout a: [T], low: Int, high: Int) {
+func quicksortRandom<T: Comparable>(_ a: inout [T], low: Int, high: Int) {
   if low < high {
     let pivotIndex = random(min: low, max: high)         // 1
 
@@ -412,7 +412,7 @@ But as you've seen with the Lomuto partitioning scheme, if the pivot occurs more
 The code for this scheme is:
 
 ```swift
-func partitionDutchFlag<T: Comparable>(inout a: [T], low: Int, high: Int, pivotIndex: Int) -> (Int, Int) {
+func partitionDutchFlag<T: Comparable>(_ a: inout [T], low: Int, high: Int, pivotIndex: Int) -> (Int, Int) {
   let pivot = a[pivotIndex]
 
   var smaller = low
@@ -461,7 +461,7 @@ Notice how the two `8`s are in the middle now. The return value from `partitionD
 Here is how you would use it in quicksort:
 
 ```swift
-func quicksortDutchFlag<T: Comparable>(inout a: [T], low: Int, high: Int) {
+func quicksortDutchFlag<T: Comparable>(_ a: inout [T], low: Int, high: Int) {
   if low < high {
     let pivotIndex = random(min: low, max: high)
     let (p, q) = partitionDutchFlag(&a, low: low, high: high, pivotIndex: pivotIndex)