[017#1]

1 files changed, 37 insertions, 0 deletions

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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";