prime.swift

//: Playground - noun: a place where people can play
import Darwin
var prime = [2, 3, 5, 7]

func isPrime(num: Int) -> Bool {
    let primeMax = Int(floor(sqrt(Double(num))))
    for i in prime {
        if i > primeMax {
            break
        }
        if num % i == 0 {
            return false
        }
    }
    return true
}

func buildPrime(max: Int) {
    let primeMax = Int(floor(sqrt(Double(max))))
    var i = 11, j = 2
    while prime[prime.count - 1] <= primeMax {
        if isPrime(num: i) {
            prime.append(i)
        }
        i = i + j
        j = 6 - j
    }
}

buildPrime(max: 1000000)
prime