Solution to Explore Swift Challenge #1

PrimeFactorSequence.swift

/*
 The code from https://gist.github.com/GarthSnyder/c8efe80675cd00322b51
 rewritten as a Swift sequence and generator.
 */

import Foundation
 
struct PrimeFactorGenerator: GeneratorType {
  var n: Int
  var divisor = 2
 
  init(_ number: Int) {
    n = number
  }
 
  mutating func next() -> Int? {
    for ; divisor <= n; ++divisor {
      if n % divisor == 0 {
        n /= divisor
        return divisor
      }
    }
    return nil
  }
}

struct PrimeFactorSequence: SequenceType {
  var n: Int
  init(_ number: Int) {
    n = number
  }

  typealias Generator = PrimeFactorGenerator
  func generate() -> Generator {
    return PrimeFactorGenerator(n)
  }
}

for i in PrimeFactorSequence(600851475143) {
  println(i)
}