Merge pull request #522 from remlostime/shuffle-swift

[Swift 4] Update Shuffle to Swift 4

Author: kelvinlauKL

Shuffle/Shuffle.playground/Contents.swift

@@ -1,40 +1,15 @@
 //: Playground - noun: a place where people can play
 
-import Foundation
-
-/* Returns a random integer between 0 and n-1. */
-public func random(_ n: Int) -> Int {
-  return Int(arc4random_uniform(UInt32(n)))
-}
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
 
-/* Fisher-Yates / Knuth shuffle */
-extension Array {
-  public mutating func shuffle() {
-    for i in stride(from: count - 1, through: 1, by: -1) {
-      let j = random(i + 1)
-      if i != j {
-        swap(&self[i], &self[j])
-      }
-    }
-  }
-}
+import Foundation
 
 var list = [ "a", "b", "c", "d", "e", "f", "g" ]
 list.shuffle()
 list.shuffle()
 list.shuffle()
 
-/* Create a new array of numbers that is already shuffled. */
-public func shuffledArray(_ n: Int) -> [Int] {
-  var a = [Int](repeating: 0, count: n)
-  for i in 0..<n {
-    let j = random(i + 1)
-    if i != j {
-      a[i] = a[j]
-    }
-    a[j] = i
-  }
-  return a
-}
-
 let numbers = shuffledArray(10)

Shuffle/Shuffle.playground/Sources/Shuffle.swift

@@ -0,0 +1,39 @@
+import Foundation
+
+/* Returns a random integer between 0 and n-1. */
+public func random(_ n: Int) -> Int {
+    return Int(arc4random_uniform(UInt32(n)))
+}
+
+extension Array {
+  /*
+    Randomly shuffles the array in-place
+    This is the Fisher-Yates algorithm, also known as the Knuth shuffle.
+    Time complexity: O(n)
+  */
+  public mutating func shuffle() {
+    for i in (1...count-1).reversed() {
+      let j = random(i + 1)
+      if i != j {
+        let t = self[i]
+        self[i] = self[j]
+        self[j] = t
+      }
+    }
+  }
+}
+
+/*
+  Simultaneously initializes an array with the values 0...n-1 and shuffles it.
+*/
+public func shuffledArray(_ n: Int) -> [Int] {
+  var a = Array(repeating: 0, count: n)
+  for i in 0..<n {
+    let j = random(i + 1)
+    if i != j {
+      a[i] = a[j]
+    }
+    a[j] = i  // insert next number from the sequence
+  }
+  return a
+}

Shuffle/Shuffle.playground/timeline.xctimeline

@@ -1,32 +1,40 @@
 import Foundation
 
+/* Returns a random integer between 0 and n-1. */
+public func random(_ n: Int) -> Int {
+    return Int(arc4random_uniform(UInt32(n)))
+}
+
 extension Array {
-  /*
-    Randomly shuffles the array in-place
-    This is the Fisher-Yates algorithm, also known as the Knuth shuffle.
-    Time complexity: O(n)
-  */
-  public mutating func shuffle() {
-    for i in (count - 1).stride(through: 1, by: -1) {
-      let j = random(i + 1)
-      if i != j {
-        swap(&self[i], &self[j])
-      }
+    /*
+     Randomly shuffles the array in-place
+     This is the Fisher-Yates algorithm, also known as the Knuth shuffle.
+     Time complexity: O(n)
+     */
+    public mutating func shuffle() {
+        for i in (1...count-1).reversed() {
+            let j = random(i + 1)
+            if i != j {
+                let t = self[i]
+                self[i] = self[j]
+                self[j] = t
+            }
+        }
     }
-  }
 }
 
 /*
-  Simultaneously initializes an array with the values 0...n-1 and shuffles it.
-*/
-public func shuffledArray(n: Int) -> [Int] {
-  var a = [Int](count: n, repeatedValue: 0)
-  for i in 0..<n {
-    let j = random(i + 1)
-    if i != j {
-      a[i] = a[j]
+ Simultaneously initializes an array with the values 0...n-1 and shuffles it.
+ */
+public func shuffledArray(_ n: Int) -> [Int] {
+    var a = Array(repeating: 0, count: n)
+    for i in 0..<n {
+        let j = random(i + 1)
+        if i != j {
+            a[i] = a[j]
+        }
+        a[j] = i  // insert next number from the sequence
     }
-    a[j] = i  // insert next number from the sequence
-  }
-  return a
+    return a
 }
+