- Added solution by Robert DiCicco.

1 files changed, 47 insertions, 0 deletions

diff --git a/challenge-137/robert-dicicco/perl/ch-1.pl b/challenge-137/robert-dicicco/perl/ch-1.pl
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+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use 5.30.0;
+
+use Date::Calc qw (leap_year Day_of_Week);
+
+# Author: Robert DiCicco
+# Date: 01-NOV-2021
+# Challenge 137
+
+# ISO-8601
+# An ISO calendar year is long if and only if the corresponding Gregorian
+# year begins on a Thursday when it is a common year or begins either on a
+# Wednesday or a Thursday when it is a leap year.
+
+# An ISO calendar year is long if and only if the corresponding Gregorian
+# year either begins or ends (or both) on a Thursday.
+
+my @years = (1900..2100);
+my @output_arr = ();
+
+foreach (@years){
+    my $leap_flag = 0;
+    if (leap_year($_)) {
+        $leap_flag = 1;
+    }
+
+    my $sdow = Day_of_Week($_, 1, 1);  # Jan. 1st  dow for selected year
+    my $ldow = Day_of_Week($_,12,31);  # Dec. 31st dow for selected year
+
+    if ($leap_flag){    # if this ia a leap year
+        if (($sdow == 3) || ($ldow == 5)){  # and the start dow is Wed., or last dow is Fri.
+            push(@output_arr, $_);  # then add to the output array
+        }
+    }
+    else { # not a leap year
+        if (($sdow == 4) || ($ldow == 4)){  # and the start dow is Thur., or last dow is Thur.
+            push(@output_arr, $_);  # then add to the output array
+        }
+    }
+}
+
+print("\n");
+print("Find all the years between 1900 and 2100 which is a Long Year.\n");
+print("Output:\n@output_arr\n");