Moved 2021 to a subdir

[aoc.git] / 2021 / 24.pl

diff --git a/2021/24.pl b/2021/24.pl
new file mode 100755 (executable)
index 0000000..de622d8
--- /dev/null
+++ b/2021/24.pl
@@ -0,0 +1,41 @@
+#!/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;
+       $visited{$_}++ for grep { /[a-z]/ } @path;
+       my $two = grep { $_ == 2 } values %visited;
+
+       for my $node (keys %{ $g{$here} }) {
+               next if $visited{$node}
+                       && ($two || $node eq 'start' || $node eq 'end');
+               my $p = join('-', @path, $node);
+               next if $subpaths{$p}++;
+               if ($node eq 'end') {
+                       push @paths, [ @path, $node ];
+                       say join('-', @path, $node);
+               } else {
+                       walk(@path, $node);
+               }
+       }
+}
+
+walk('start');
+
+say scalar @paths;
+               
+