Greatest Common Divisor - Euclidean algorithm

def gcd(a, b)
    if b > a
        temp = a
        a = b
        b = temp
    end
    mod = a % b
    if mod == 0 
        return b
    else
        return gcd(b, mod)
    end
end

p gcd(210, 45) #15

p gcd(1, 1) #1