[013#2]

1 files changed, 38 insertions, 0 deletions

diff --git a/013/ch2.pl b/013/ch2.pl
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+#!/usr/bin/env perl
+#
+# Write a script to demonstrate Mutually Recursive methods. Two methods are
+# mutually recursive if the first method calls the second and the second calls
+# first in turn. Using the mutually recursive methods, generate Hofstadter
+# Female and Male sequences.
+# (https://en.wikipedia.org/wiki/Hofstadter_sequence#Hofstadter_Female_and_Male_sequences)
+################################################################################
+
+use strict;
+use warnings;
+
+use Memoize qw<memoize>;
+
+# Cache the results of previous computations
+memoize('M');
+memoize('F');
+
+sub M {
+    my $n = shift;
+    return $n == 0
+        ? 0
+        : $n - F(M($n-1));
+}
+
+sub F {
+    my $n = shift;
+    return $n == 0
+        ? 1
+        : $n - M(F($n-1));
+}
+
+die "Usage: $0 <iterations>\n" unless @ARGV == 1;
+
+print "M\tF\n-\t-\n";
+foreach my $n (0 .. shift) {
+    printf "%d\t%d\n", M($n), F($n);
+}