Moved 2021 to a subdir

[aoc.git] / 2021 / 23.pl

diff --git a/2021/23.pl b/2021/23.pl
new file mode 100755 (executable)
index 0000000..1cb99a6
--- /dev/null
+++ b/2021/23.pl
@@ -0,0 +1,38 @@
+#!/usr/bin/perl -w
+
+use v5.16;
+
+my %g;
+while (<>) {
+       chomp;
+       my ($n1, $n2) = split /-/;
+       $g{$n1}->{$n2} = 1;
+       $g{$n2}->{$n1} = 1;
+}
+
+my @paths;
+my %subpaths;
+
+sub walk {
+       my (@path) = @_;
+       my $here = $path[-1];
+       my %visited = map { $_ => 1 } grep { /[a-z]/ } @path;
+
+       for my $node (keys %{ $g{$here} }) {
+               next if $visited{$node};
+               if ($node eq 'end') {
+                       push @paths, [ @path, $node ];
+                       say join('-', @{ $paths[-1] });
+               } else {
+                       my $p = join('-', @path, $node);
+                       next if $subpaths{$p}++;
+                       walk(@path, $node);
+               }
+       }
+}
+
+walk('start');
+
+say scalar @paths;
+               
+