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"""This module contains a code example related to

Think Python, 2nd Edition

by Allen Downey

http://thinkpython2.com

Copyright 2015 Allen Downey

License: http://creativecommons.org/licenses/by/4.0/

"""

from __future__ import print_function, division

cache = {}

def ackermann(m, n):

"""Computes the Ackermann function A(m, n)

See http://en.wikipedia.org/wiki/Ackermann_function

n, m: non-negative integers

"""

if m == 0:

return n+1

if n == 0:

return ackermann(m-1, 1)

if (m, n) in cache:

return cache[m, n]

else:

cache[m, n] = ackermann(m-1, ackermann(m, n-1))

return cache[m, n]

print(ackermann(3, 4))

print(ackermann(3, 6))