Day 23: quite slow to write

diff --git a/2023/45.pl b/2023/45.pl
new file mode 100755 (executable)
index 0000000..28185b8
--- /dev/null
+++ b/2023/45.pl
@@ -0,0 +1,41 @@
+#!/usr/bin/perl -w
+
+use v5.38;
+use experimental 'multidimensional';
+$; = ',';
+
+my @map = map { chomp; [ split // ] } <>;
+my $xmax = $#{ $map[0] };
+my $ymax = $#map;
+
+my @dx = (1, 0, -1, 0);
+my @dy = (0, 1, 0, -1);
+
+my %seen;
+my @q = [ 1, 1, 1, [1, 1] ];
+while (@q) {
+       my ($x, $y, $steps, @path) = @{ shift @q };
+
+       next if $seen{$x,$y} && $seen{$x,$y} > $steps;
+       $seen{$x,$y} = $steps;
+       if ($x == $xmax-1 && $y == $ymax) {
+               say "at $x,$y, $steps, ", join(' ', map { "[$_->[0],$_->[1]]" } @path);
+               say "path len $steps";
+               next;
+       }
+       my %visited;
+       $visited{$_->[0],$_->[1]} = 1 for @path;
+       for my $d (0 .. 3) {
+               my $nx = $x + $dx[$d];
+               my $ny = $y + $dy[$d];
+               next if $map[$ny][$nx] eq '#';
+               next if $ny == 0;
+               next if $visited{$nx,$ny};
+               next if $d != 0 && $map[$y][$x] eq '>';
+               next if $d != 1 && $map[$y][$x] eq 'v';
+               next if $d != 2 && $map[$y][$x] eq '<';
+               next if $d != 3 && $map[$y][$x] eq '^';
+               push @q, [ $nx, $ny, $steps+1, @path, [ $nx, $ny ] ];
+       }
+}
+

diff --git a/2023/46.pl b/2023/46.pl
new file mode 100755 (executable)
index 0000000..e6e8471
--- /dev/null
+++ b/2023/46.pl
@@ -0,0 +1,90 @@
+#!/usr/bin/perl -w
+
+use v5.38;
+use experimental 'multidimensional';
+use Array::Heap;
+$; = ',';
+
+my @map = map { chomp; y/<>^v/..../; [ split // ] } <>;
+my $xmax = $#{ $map[0] };
+my $ymax = $#map;
+
+my @dx = (1, 0, -1, 0);
+my @dy = (0, 1, 0, -1);
+
+my @crossings = ([1, 0], [$xmax-1, $ymax]);
+
+for my $y (1 .. $ymax-1) {
+       for my $x (1 .. $xmax-1) {
+               next if $map[$y][$x] ne '.';
+               my $cnt;
+               for my $d (0 .. 3) {
+                       my $nx = $x + $dx[$d];
+                       my $ny = $y + $dy[$d];
+                       $cnt++ if $map[$ny][$nx] eq '.';
+               }
+               next if $cnt <= 2;
+               say "cross ", scalar @crossings, " at $x,$y: $cnt";
+               push @crossings, [$x,$y];
+       }
+}
+
+my %is_cross;
+for (0 .. $#crossings) {
+       $is_cross{$crossings[$_]->[0],$crossings[$_]->[1]} = $_;
+}
+
+my %xnei;
+
+my %seen;
+my @q = [ 1, 1, 0, 0, 0 ];
+while (@q) {
+       my ($x, $y, $len, $prevx, $prevdist) = @{ shift @q };
+       
+       if (defined $is_cross{$x,$y}) {
+               my $self = $is_cross{$x,$y};
+               if (defined $prevx) {
+                       if ($self != $prevx) {
+                               my $l = $len - $prevdist;
+                               say "$prevx-$self $l";
+                               $xnei{$self}{$prevx} = $l;
+                               $xnei{$prevx}{$self} = $l;
+                       }
+               }
+               $prevx = $self;
+               $prevdist = $len;
+       }
+       next if $seen{$x,$y,$prevx}++;
+
+       for my $d (0 .. 3) {
+               my $nx = $x + $dx[$d];
+               my $ny = $y + $dy[$d];
+               next if $ny == 0;
+               next if $ny > $ymax;
+               next if $map[$ny][$nx] eq '#';
+               push @q, [$nx, $ny, $len+1, $prevx, $prevdist];
+       }
+}
+
+my $maxlen = 0;
+%seen = ();
+sub walk {
+       my ($self, $dist) = @_;
+
+       # say "at $self $dist @path";
+       if ($self == 1) {
+               if ($maxlen < $dist) {
+                       $maxlen = $dist;
+                       say "$dist";
+               }
+       }
+       $seen{$self} = 1;
+       for my $nxt (keys %{ $xnei{$self} }) {
+               next if $seen{$nxt};
+               walk($nxt, $dist + $xnei{$self}{$nxt});
+       }
+       $seen{$self} = 0;
+}
+
+walk(0, 1);
+