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+#!/usr/bin/env perl
+
+# Perl Weekly Challenge 013-1
+
+# 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
+
+# I should not have read the challenge during the start of TPC
+
+use strict;
+use warnings;
+use utf8;
+use feature qw{ postderef say signatures state switch };
+no warnings
+    qw{ experimental::postderef experimental::smartmatch experimental::signatures };
+
+use DateTime;
+
+my $year = shift @ARGV;
+$year //= 2019; # because sawyer x mentioned the //= operator to applause
+
+last_fridays($year);
+
+# best to not think of this in terms of the year, but as 12 
+# instances of last friday in the month
+sub last_fridays ( $year ) {
+    for my $mon ( 1 .. 12 ) { say last_friday( $year, $mon ); }
+}
+
+sub last_friday ( $year, $mon ) {
+    # Thank you Dave Rolsky and everyone else who made this simple
+
+    # Months are not of a standard size. We don't know the last day
+    # but we do know what the first day is
+    my $dt = DateTime->new(
+        year      => $year,
+        month     => $mon,
+        day       => 1,
+        hour      => 12,
+        minute    => 0,
+        second    => 0,
+        time_zone => 'floating'
+    );
+
+    # and no month is 32 days long
+    $dt->add( days => 32 );
+
+    # while does nothing if the test is true
+    $dt->subtract( days => 1 ) while $dt->day_of_week != 5; # find a friday
+    $dt->subtract( days => 7 ) while $dt->month != $mon;    # and move backto the right month
+    return $dt->ymd('/'); # example solution uses slashes
+}
+
+__DATA__
+
+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