--- /dev/null
+#!/usr/bin/perl -w
+
+use v5.36;
+use strict;
+
+my %map;
+my $base = 1_000_000;
+my @el;
+
+my $y = $base;
+while (<>) {
+ chomp;
+ my $x = $base;
+ for my $pt (split //) {
+ if ($pt eq '#') {
+ $map{"$x,$y"} = 1;
+ push @el, [ $x, $y, 0 ];
+ }
+ $x++;
+ }
+ $y++;
+}
+
+sub occupied($map, $x, $y) {
+ return $map->{"$x,$y"};
+}
+
+my ($xmin, $xmax, $ymin, $ymax);
+
+my $round = 0;
+while ($round < 10) {
+ say "round ", ++$round;
+ my %prop;
+ my @prop;
+ for my $i (0 .. $#el) {
+ my ($x, $y, $state) = @{ $el[$i] };
+ my $prop;
+ my $sum = -1;
+ for my $x1 ($x-1 .. $x+1) {
+ for my $y1 ($y-1 .. $y+1) {
+ $sum++ if $map{"$x1,$y1"};
+ }
+ }
+ next if !$sum;
+ DIR:
+ for my $add (0 .. 3) {
+ my $dir = ($add + $state) % 4;
+ if ($dir == 0) {
+ for my $x1 ($x-1 .. $x+1) {
+ next DIR if occupied(\%map, $x1, $y-1);
+ }
+ $prop = [ $x, $y-1, 1, $i ];
+ last;
+ } elsif ($dir == 1) {
+ for my $x1 ($x-1 .. $x+1) {
+ next DIR if occupied(\%map, $x1, $y+1);
+ }
+ $prop = [ $x, $y+1, 2, $i ];
+ last;
+ } elsif ($dir == 2) {
+ for my $y1 ($y-1 .. $y+1) {
+ next DIR if occupied(\%map, $x-1, $y1);
+ }
+ $prop = [ $x-1, $y, 3, $i ];
+ last;
+ } elsif ($dir == 3) {
+ for my $y1 ($y-1 .. $y+1) {
+ next DIR if occupied(\%map, $x+1, $y1);
+ }
+ $prop = [ $x+1, $y, 0, $i ];
+ last;
+ }
+ }
+ if ($prop) {
+ $prop[$i] = $prop;
+ $prop{"$prop->[0],$prop->[1]"}++;
+ }
+ }
+ last if !@prop;
+ for my $i (0 .. $#prop) {
+ my $p = $prop[$i];
+ next if !defined $p;
+ my ($x1, $y1) = @$p;
+ my ($x, $y) = @{ $el[$i] };
+ if ($prop{"$x1,$y1"} != 1) {
+ next;
+ }
+ undef $map{"$x,$y"};
+ $map{"$x1,$y1"} = 1;
+ $el[$i][0] = $x1;
+ $el[$i][1] = $y1;
+ }
+ ($xmin, $xmax, $ymin, $ymax) = (undef, undef, undef, undef);
+ for my $e (@el) {
+ my ($x, $y) = @$e;
+ $xmin = $x if !defined $xmin || $xmin > $x;
+ $ymin = $y if !defined $ymin || $ymin > $y;
+ $xmax = $x if !defined $xmax || $xmax < $x;
+ $ymax = $y if !defined $ymax || $ymax < $y;
+ $e->[2]++;
+ $e->[2] %= 4;
+ }
+}
+
+say (($xmax - $xmin + 1) * ($ymax - $ymin + 1) - @el);
+
--- /dev/null
+#!/usr/bin/perl -w
+
+use v5.36;
+use strict;
+
+my %map;
+my $base = 1_000_000;
+my @el;
+
+my $y = $base;
+while (<>) {
+ chomp;
+ my $x = $base;
+ for my $pt (split //) {
+ if ($pt eq '#') {
+ $map{"$x,$y"} = 1;
+ push @el, [ $x, $y, 0 ];
+ }
+ $x++;
+ }
+ $y++;
+}
+
+sub occupied($map, $x, $y) {
+ return $map->{"$x,$y"};
+}
+
+my ($xmin, $xmax, $ymin, $ymax);
+
+my $moved = 1;
+my $round = 0;
+while (1) {
+ say "round ", ++$round;
+ my %prop;
+ my @prop;
+ for my $i (0 .. $#el) {
+ my ($x, $y, $state) = @{ $el[$i] };
+ my $prop;
+ my $sum = -1;
+ for my $x1 ($x-1 .. $x+1) {
+ for my $y1 ($y-1 .. $y+1) {
+ $sum++ if $map{"$x1,$y1"};
+ }
+ }
+ next if !$sum;
+ DIR:
+ for my $add (0 .. 3) {
+ my $dir = ($add + $state) % 4;
+ if ($dir == 0) {
+ for my $x1 ($x-1 .. $x+1) {
+ next DIR if occupied(\%map, $x1, $y-1);
+ }
+ $prop = [ $x, $y-1, 1, $i ];
+ last;
+ } elsif ($dir == 1) {
+ for my $x1 ($x-1 .. $x+1) {
+ next DIR if occupied(\%map, $x1, $y+1);
+ }
+ $prop = [ $x, $y+1, 2, $i ];
+ last;
+ } elsif ($dir == 2) {
+ for my $y1 ($y-1 .. $y+1) {
+ next DIR if occupied(\%map, $x-1, $y1);
+ }
+ $prop = [ $x-1, $y, 3, $i ];
+ last;
+ } elsif ($dir == 3) {
+ for my $y1 ($y-1 .. $y+1) {
+ next DIR if occupied(\%map, $x+1, $y1);
+ }
+ $prop = [ $x+1, $y, 0, $i ];
+ last;
+ }
+ }
+ if ($prop) {
+ $prop[$i] = $prop;
+ $prop{"$prop->[0],$prop->[1]"}++;
+ }
+ }
+ last if !@prop;
+ $moved = 0;
+ for my $i (0 .. $#prop) {
+ my $p = $prop[$i];
+ next if !defined $p;
+ my ($x1, $y1) = @$p;
+ my ($x, $y) = @{ $el[$i] };
+ if ($prop{"$x1,$y1"} != 1) {
+ #say "$i not moving $x,$y -> $x1,$y1";
+ next;
+ }
+ $moved++;
+ #say "$i moved $x,$y -> $x1,$y1";
+ undef $map{"$x,$y"};
+ $map{"$x1,$y1"} = 1;
+ $el[$i][0] = $x1;
+ $el[$i][1] = $y1;
+ }
+ ($xmin, $xmax, $ymin, $ymax) = (undef, undef, undef, undef);
+ for my $e (@el) {
+ my ($x, $y) = @$e;
+ $xmin = $x if !defined $xmin || $xmin > $x;
+ $ymin = $y if !defined $ymin || $ymin > $y;
+ $xmax = $x if !defined $xmax || $xmax < $x;
+ $ymax = $y if !defined $ymax || $ymax < $y;
+ $e->[2]++;
+ $e->[2] %= 4;
+ }
+ say "$xmin .. $xmax, $ymin .. $ymax";
+}
+
+say "result $xmin .. $xmax $ymin .. $ymax";
+say $round;