Day 16: beam reflections

[aoc.git] / 2023 / 31.pl

diff --git a/2023/31.pl b/2023/31.pl
new file mode 100755 (executable)
index 0000000..bf4af15
--- /dev/null
+++ b/2023/31.pl
@@ -0,0 +1,43 @@
+#!/usr/bin/perl -w
+
+use v5.38;
+use experimental 'multidimensional';
+$; = ';';
+
+my @map = map { chomp; [ split // ] } <>;
+my $xmax = $#{ $map[0] };
+my $ymax = $#map;
+
+my @dirs = ([1, 0], [0, 1], [-1, 0], [0, -1]);
+
+my %seen;
+my @q = [-1, 0, 0];
+
+my @slash = (3, 2, 1, 0);
+my @bs    = (1, 0, 3, 2);
+
+while (@q) {
+       my ($x, $y, $dir) = @{ shift @q };
+       my ($dx, $dy) = @{ $dirs[$dir] };
+
+       $x += $dx; $y += $dy;
+       next if $x < 0 || $y < 0 || $x > $xmax || $y > $ymax;
+
+       next if $seen{$x,$y} && ($seen{$x,$y} & (1 << $dir));
+       $seen{$x,$y} |= (1 << $dir);
+
+       my $pt = $map[$y][$x];
+       if ($pt eq '-' && ($dir == 1 || $dir == 3)) {
+               push @q, [$x, $y, 0], [$x, $y, 2];
+       } elsif ($pt eq '|' && ($dir == 0 || $dir == 2)) {
+               push @q, [$x, $y, 1], [$x, $y, 3];
+       } elsif ($pt eq '/') {
+               push @q, [$x, $y, $slash[$dir]];
+       } elsif ($pt eq '\\') {
+               push @q, [$x, $y, $bs[$dir]];
+       } else {
+               push @q, [$x, $y, $dir];
+       }
+}
+
+say scalar keys %seen;