Updated syntax to Swift 3

Author: richard-ash

Karatsuba Multiplication/KaratsubaMultiplication.playground/Contents.swift

@@ -2,17 +2,23 @@
 
 import Foundation
 
-infix operator ^^ { associativity left precedence 160 }
+precedencegroup ExponentiativePrecedence {
+  higherThan: MultiplicationPrecedence
+  lowerThan: BitwiseShiftPrecedence
+  associativity: left
+}
+
+infix operator ^^: ExponentiativePrecedence
 func ^^ (radix: Int, power: Int) -> Int {
   return Int(pow(Double(radix), Double(power)))
 }
 
 // Long Multiplication - O(n^2)
-func multiply(num1: Int, _ num2: Int, base: Int = 10) -> Int {
-  let num1Array = String(num1).characters.reverse().map{ Int(String($0))! }
-  let num2Array = String(num2).characters.reverse().map{ Int(String($0))! }
+func multiply(_ num1: Int, by num2: Int, base: Int = 10) -> Int {
+  let num1Array = String(num1).characters.reversed().map{ Int(String($0))! }
+  let num2Array = String(num2).characters.reversed().map{ Int(String($0))! }
 
-  var product = Array(count: num1Array.count + num2Array.count, repeatedValue: 0)
+  var product = Array(repeating: 0, count: num1Array.count + num2Array.count)
 
   for i in num1Array.indices {
     var carry = 0
@@ -24,16 +30,16 @@ func multiply(num1: Int, _ num2: Int, base: Int = 10) -> Int {
     product[i + num2Array.count] += carry
   }
 
-  return Int(product.reverse().map{ String($0) }.reduce("", combine: +))!
+  return Int(product.reversed().map{ String($0) }.reduce("", +))!
 }
 
 // Karatsuba Multiplication - O(nlogn)
-func karatsuba(num1: Int, _ num2: Int) -> Int {
+func karatsuba(_ num1: Int, by num2: Int) -> Int {
   let num1Array = String(num1).characters
   let num2Array = String(num2).characters
 
   guard num1Array.count > 1 && num2Array.count > 1 else {
-    return multiply(num1, num2)
+    return multiply(num1, by: num2)
   }
 
   let n = max(num1Array.count, num2Array.count)
@@ -44,14 +50,12 @@ func karatsuba(num1: Int, _ num2: Int) -> Int {
   let c = num2 / 10^^nBy2
   let d = num2 % 10^^nBy2
 
-  let ac = karatsuba(a, c)
-  let bd = karatsuba(b, d)
-  let adPluscd = karatsuba(a+b, c+d) - ac - bd
+  let ac = karatsuba(a, by: c)
+  let bd = karatsuba(b, by: d)
+  let adPluscd = karatsuba(a+b, by: c+d) - ac - bd
 
   let product = ac * 10^^(2 * nBy2) + adPluscd * 10^^nBy2 + bd
 
   return product
 }
 
-print(multiply(236742342, 1231234224))
-print(karatsuba(236742342, 1231234224))

Karatsuba Multiplication/KaratsubaMultiplication.swift

@@ -8,7 +8,18 @@
 
 import Foundation
 
-func karatsuba(num1: Int, _ num2: Int) -> Int {
+precedencegroup ExponentiativePrecedence {
+  higherThan: MultiplicationPrecedence
+  lowerThan: BitwiseShiftPrecedence
+  associativity: left
+}
+
+infix operator ^^: ExponentiativePrecedence
+func ^^ (radix: Int, power: Int) -> Int {
+  return Int(pow(Double(radix), Double(power)))
+}
+
+func karatsuba(_ num1: Int, by num2: Int) -> Int {
   let num1Array = String(num1).characters
   let num2Array = String(num2).characters
 
@@ -24,11 +35,11 @@ func karatsuba(num1: Int, _ num2: Int) -> Int {
   let c = num2 / 10^^nBy2
   let d = num2 % 10^^nBy2
 
-  let ac = karatsuba(a, c)
-  let bd = karatsuba(b, d)
-  let adPluscd = karatsuba(a+b, c+d) - ac - bd
+  let ac = karatsuba(a, by: c)
+  let bd = karatsuba(b, by: d)
+  let adPluscd = karatsuba(a+b, by: c+d) - ac - bd
 
   let product = ac * 10^^(2 * nBy2) + adPluscd * 10^^nBy2 + bd
 
   return product
-}
+}