Week 227 Task 1

1 files changed, 50 insertions, 0 deletions

diff --git a/challenge-227/cheok-yin-fung/perl/ch-1.pl b/challenge-227/cheok-yin-fung/perl/ch-1.pl
new file mode 100644
index 0000000000..18013f6491
--- /dev/null
+++ b/challenge-227/cheok-yin-fung/perl/ch-1.pl
@@ -0,0 +1,50 @@
+use v5.30.0;
+use warnings;
+use List::Util qw/reductions/;
+
+sub is_leap_year {
+    my $year = $_[0];
+    return 1 if ($year % 4 == 0 && $year % 100 != 0) || $year % 400 == 0;
+    return 0;
+}
+
+my @mon = (31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30);
+my @mon_ly = (31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30);
+
+# https://en.wikipedia.org/wiki/Zeller%27s_congruence
+sub zeller_cong {
+    my @day_of_week = ("Sat", "Sun", "Mon", "Tue", "Wed", "Thu", "Fri");
+    my $year = $_[0];
+    my $m = $_[1];
+    my $q = $_[2];
+    if ($m < 3) {
+        $m = 13 if $m == 1;
+        $m = 14 if $m == 2;
+        $year = $year - 1;
+    }
+    my $J = int($year/100);
+    my $K = $year % 100;
+    my $h = ($q + int(13*($m+1)/5) + $K + int($K/4) + int($J/4) - 2*$J) % 7;
+    return ($h+6) % 7;
+}
+
+sub num_of_black_fri {
+    my $year = $_[0];
+    my @arr = ();
+    push @arr, zeller_cong($year, 1, 13);
+    if (is_leap_year($year)) {
+        @arr = reductions {$a+$b} @arr, @mon_ly;
+    }
+    else {
+        @arr = reductions {$a+$b} @arr, @mon;
+    }
+    @arr = map {$_ % 7} @arr;
+    return grep {$_ == 5} @arr;
+}
+
+use Test::More tests=>4;
+# https://robslink.com/SAS/democd42/friday13.htm
+ok num_of_black_fri(2023) == 2;
+ok num_of_black_fri(2024) == 2;
+ok num_of_black_fri(2025) == 1;
+ok num_of_black_fri(2026) == 3;