4 use experimental 'multidimensional';
7 my @map = map { chomp; [ split // ] } <>;
8 my $xmax = $#{ $map[0] };
11 my @dirs = ([1, 0], [0, 1], [-1, 0], [0, -1]);
16 my @slash = (3, 2, 1, 0);
17 my @bs = (1, 0, 3, 2);
20 my ($x, $y, $dir) = @{ shift @q };
21 my ($dx, $dy) = @{ $dirs[$dir] };
24 next if $x < 0 || $y < 0 || $x > $xmax || $y > $ymax;
26 next if $seen{$x,$y} && ($seen{$x,$y} & (1 << $dir));
27 $seen{$x,$y} |= (1 << $dir);
29 my $pt = $map[$y][$x];
30 if ($pt eq '-' && ($dir == 1 || $dir == 3)) {
31 push @q, [$x, $y, 0], [$x, $y, 2];
32 } elsif ($pt eq '|' && ($dir == 0 || $dir == 2)) {
33 push @q, [$x, $y, 1], [$x, $y, 3];
34 } elsif ($pt eq '/') {
35 push @q, [$x, $y, $slash[$dir]];
36 } elsif ($pt eq '\\') {
37 push @q, [$x, $y, $bs[$dir]];
39 push @q, [$x, $y, $dir];
43 say scalar keys %seen;