https://projecteuler.net/problem=14

euler14.py

#!/usr/bin/env pypy

import time


n = 13
# n = 1000000


if __name__ == "__main__":
    def calc(n):
        global g_max
        g_max += 1

        if n == 1:
            return 1
        elif n % 2 == 0:
            return calc(n/2)
        else:
            return calc(3*n + 1)

    start = time.time()

    max_x = 0
    max_count = 0

    for x in xrange(n, 1, -1):
        g_max = 0
        calc(x)

        if g_max > max_count:
            max_x = x
            max_count = g_max

    print max_x, max_count

    end = time.time()
    print end-start