Year 2018

[aoc.git] / 2018 / 04.pl

diff --git a/2018/04.pl b/2018/04.pl
new file mode 100755 (executable)
index 0000000..dca4189
--- /dev/null
+++ b/2018/04.pl
@@ -0,0 +1,22 @@
+#!/usr/bin/perl -w
+
+use v5.30;
+use strict;
+
+my %seen;
+while (<>) {
+       chomp;
+       for my $i (0 .. length($_) - 1) {
+               my $x = $_;
+               substr($x, $i, 1) = '_';
+               $seen{$x}++;
+       }
+}
+
+for my $k (keys %seen) {
+       if ($seen{$k} == 2) {
+               $k =~ s/_//;
+               say $k;
+       }
+}
+