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#!/usr/bin/env perl
#
# Create a script to demonstrate Ackermann function. The Ackermann function is
# defined as below, m and n are positive number:
#
# A(m, n) = n + 1 if m = 0
# A(m, n) = A(m - 1, 1) if m > 0 and n = 0
# A(m, n) = A(m - 1, A(m, n - 1)) if m > 0 and n > 0
#
# Example expansions as shown in wiki page.
#
# A(1, 2) = A(0, A(1, 1))
# = A(0, A(0, A(1, 0)))
# = A(0, A(0, A(0, 1)))
# = A(0, A(0, 2))
# = A(0, 3)
# = 4
#
# (https://en.wikipedia.org/wiki/Ackermann_function).
################################################################################
use strict;
use warnings;
use Memoize;
memoize "ack";
sub ack {
my ($m, $n) = @_;
return $n+1 if $m == 0;
return ack($m-1, 1) if $n == 0;
return ack($m-1, ack($m, $n-1));
}
@ARGV == 2 || die "Usage: $0 <m> <n>\n";
print ack(@ARGV), "\n";
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