3 files changed, 80 insertions, 0 deletions
diff --git a/challenge-013/yozen-hernandez/blog.txt b/challenge-013/yozen-hernandez/blog.txt
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@@ -0,0 +1 @@
+https://yzhernand.github.io/posts/perl-weekly-challenge-13/
diff --git a/challenge-013/yozen-hernandez/perl5/ch-1.pl b/challenge-013/yozen-hernandez/perl5/ch-1.pl
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+++ b/challenge-013/yozen-hernandez/perl5/ch-1.pl
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+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw(say state);
+use DateTime;
+use DateTime::Duration;
+
+# Write a script to print the date of last Friday of every month of a given
+# year. For example, if the given year is 2019 then it should print the
+# following:
+#
+# 2019/01/25
+# 2019/02/22
+# 2019/03/29
+# 2019/04/26
+# 2019/05/31
+# 2019/06/28
+# 2019/07/26
+# 2019/08/30
+# 2019/09/27
+# 2019/10/25
+# 2019/11/29
+# 2019/12/27
+ 
+my $year = shift or die "Usage: $0 <year>\n";
+
+my $dt = DateTime->new(
+    month => 1,
+    day   => 1,
+    year  => $year
+);
+my $add_week = DateTime::Duration->new( weeks => 1 );
+my $add_day  = DateTime::Duration->new( days  => 1 );
+
+while ( $dt->day_of_week() != 5 ) { $dt->add($add_day); }
+
+my %last_fri;
+while ( $dt->year == $year ) {
+    $last_fri{ $dt->month } = $dt->ymd("/");
+    $dt->add($add_week);
+}
+
+{
+    local $, = "\n";
+    say @last_fri{ sort { $a <=> $b } keys %last_fri };
+}
diff --git a/challenge-013/yozen-hernandez/perl5/ch-2.pl b/challenge-013/yozen-hernandez/perl5/ch-2.pl
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index 0000000000..dcb92bb32b
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+++ b/challenge-013/yozen-hernandez/perl5/ch-2.pl
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+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw(say state);
+use Carp;
+
+# 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.
+
+sub hofstadter_F {
+    my $n = shift;
+    state %cache = ( 0 => 1 );
+
+    return $cache{$n} if exists $cache{$n};
+    return $cache{$n} = $n - hofstadter_M( hofstadter_F( $n - 1 ) );
+}
+
+sub hofstadter_M {
+    my $n = shift;
+    state %cache = ( 0 => 0 );
+
+    return $cache{$n} if exists $cache{$n};
+    return $cache{$n} = $n - hofstadter_F( hofstadter_M( $n - 1 ) );
+}
+
+my $n = shift or die "Usage: $0 <n>\n";
+
+say "F: ", join( ", ", map { hofstadter_F($_) } ( 0 .. $n ) );
+say "M: ", join( ", ", map { hofstadter_M($_) } ( 0 .. $n ) );