Challenge 019 task 1

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diff --git a/challenge-019/jo-37/perl/ch-1.pl b/challenge-019/jo-37/perl/ch-1.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use warnings;
+use Date::Manip::Recur;
+
+main: {
+    # A month with five Fridays and five Sundays has five Saturdays,
+    # too.
+
+    # Find all months having five Fridays.
+    my @fridays = map $_->printf('%Y/%m'),
+        Date::Manip::Recur->new('5th Friday of every month',
+        undef, 1900, 2020)->dates;
+    # Find all months having five Sundays.
+    my @sundays = map $_->printf('%Y/%m'),
+        Date::Manip::Recur->new('5th Sunday of every month',
+        undef, 1900, 2020)->dates;
+
+    # Build a hash having the months with five Fridays as keys and
+    # values.
+    my %fridays;
+    @fridays{@fridays} = @fridays;
+    # Find the intersection between months with five Fridays and five
+    # Sundays.
+    say for grep defined, @fridays{@sundays};
+}