Day 25: keys and locks

diff --git a/2024/49.pl b/2024/49.pl
new file mode 100755 (executable)
index 0000000..ef8069a
--- /dev/null
+++ b/2024/49.pl
@@ -0,0 +1,19 @@
+#!/usr/bin/perl -w
+
+use v5.40;
+
+$/ = "\n\n";
+my @keys = <>;
+
+my $pairs;
+for my ($i, $k1) (indexed @keys) {
+       K2:
+       for my $k2 (@keys[$i+1 .. $#keys]) {
+               for my $i (0 .. length $k1) {
+                       next K2 if substr($k1, $i, 1) eq '#'
+                               && substr($k2, $i, 1) eq '#';
+               }
+               $pairs++;
+       }
+}
+say $pairs;