Recursive greatest common divider

gistfile1.swift

func greatestCommonDivisor(first: Int, second: Int) -> Int {
    return internalPrivateGreatestCommonDivisor(first, second, min(first, second))
}

private func internalPrivateGreatestCommonDivisor(first: Int, second: Int, divider: Int) -> Int {
    
    if divider == 0 {
        return 0
    }
    
    if (first % divider == 0) &&
       (second % divider == 0) {
        return divider
    }
    
    return internalPrivateGreatestCommonDivisor(first, second, divider-1)
}