"""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))
