from __future__ import absolute_import
from __future__ import division
from __future__ import print_function


def gcd(m, n):
    """Greatest Common Divisor (GCD) by Euclid's Algorithm.

    Time complexity: O(m%n).
    Space complexity: O(1).
    """
    while n != 0:
        m, n = n, m % n
    return m


def main():
    print('gcd(4, 2): {}'.format(gcd(4, 2)))
    print('gcd(2, 4): {}'.format(gcd(2, 4)))

    print('gcd(10, 4): {}'.format(gcd(10, 4)))
    print('gcd(4, 10): {}'.format(gcd(4, 10)))

    print('gcd(3, 4): {}'.format(gcd(3, 4)))
    print('gcd(4, 3): {}'.format(gcd(4, 3)))


if __name__ == '__main__':
    main()

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function


def gcd_recur(m, n):
    """Greatest Common Divisor (GCD) by Euclid's Algorithm.

    Time complexity: O(m%n).
    Space complexity: O(m%n).
    """
    if n == 0:
        return m
    return gcd_recur(n, m % n)


def gcd_iter(m, n):
    """Greatest Common Divisor (GCD) by Euclid's Algorithm.

    Time complexity: O(m%n).
    Space complexity: O(1).
    """
    while n != 0:
        m, n = n, m % n
    return m


def main():
    import time

    start_time = time.time()
    print('gcd_recur(4, 2): {}'.format(gcd_recur(4, 2)))
    print('gcd_recur(2, 4): {}'.format(gcd_recur(2, 4)))
    print('gcd_recur(10, 4): {}'.format(gcd_recur(10, 4)))
    print('gcd_recur(4, 10): {}'.format(gcd_recur(4, 10)))
    print('gcd_recur(3, 4): {}'.format(gcd_recur(3, 4)))
    print('gcd_recur(4, 3): {}'.format(gcd_recur(4, 3)))
    print('Time:', time.time() - start_time)

    start_time = time.time()
    print('gcd_iter(4, 2): {}'.format(gcd_iter(4, 2)))
    print('gcd_iter(2, 4): {}'.format(gcd_iter(2, 4)))
    print('gcd_iter(10, 4): {}'.format(gcd_iter(10, 4)))
    print('gcd_iter(4, 10): {}'.format(gcd_iter(4, 10)))
    print('gcd_iter(3, 4): {}'.format(gcd_iter(3, 4)))
    print('gcd_iter(4, 3): {}'.format(gcd_iter(4, 3)))
    print('Time:', time.time() - start_time)


if __name__ == '__main__':
    main()

Complete gcd recur sol w/ time/space complexity