Day 22: slow but straightforward. off-by-three errors.

[aoc.git] / 2023 / 44.pl

diff --git a/2023/44.pl b/2023/44.pl
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index 0000000..e8ee0c7
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+++ b/2023/44.pl
@@ -0,0 +1,88 @@
+#!/usr/bin/perl -w
+
+use v5.38;
+use experimental 'multidimensional';
+$; = ';';
+
+my @bricks = map { [ /\d+/g ] } <>;
+my %seen;
+sub set_brick {
+       my ($b) = @_;
+
+       for my $x ($b->[0] .. $b->[3]) {
+       for my $y ($b->[1] .. $b->[4]) {
+       for my $z ($b->[2] .. $b->[5]) {
+               $seen{$x,$y,$z} = 1;
+       } } }
+}
+
+sub clr_brick {
+       my ($b) = @_;
+
+       for my $x ($b->[0] .. $b->[3]) {
+       for my $y ($b->[1] .. $b->[4]) {
+       for my $z ($b->[2] .. $b->[5]) {
+               undef $seen{$x,$y,$z};
+       } } }
+}
+
+sub can_fall {
+       my ($b) = @_;
+
+       return undef if !$b->[2];
+       my $z = $b->[2]-1;
+
+       for my $x ($b->[0] .. $b->[3]) {
+       for my $y ($b->[1] .. $b->[4]) {
+               return undef if $seen{$x,$y,$z};
+       } }
+       return 1;
+}
+
+set_brick($_) for @bricks;
+
+while (1) {
+       my $fallen;
+       my $i = 0;
+       for my $b (@bricks) {
+               $i++;
+               next if !can_fall($b);
+               # say "falling $i (@$b)";
+               clr_brick($b);
+               $b->[2]--; $b->[5]--;
+               set_brick($b);
+               # say "fallen  $i (@$b)";
+               $fallen++;
+       }
+       last if !$fallen;
+}
+
+my $sum;
+SBRICK:
+for my $bi0 (0 .. $#bricks) {
+       my @bricks1 = map { [ @$_ ] } @bricks;
+       splice @bricks1, $bi0, 1;
+       %seen = ();
+       set_brick($_) for @bricks1;
+       my %f;
+       while (1) {
+               my $fallen;
+               my $i = 0;
+               for my $bi1 (0 .. $#bricks1) {
+                       my $b1 = $bricks1[$bi1];
+                       next if !can_fall($b1);
+                       # say "falling $i (@$b1)";
+                       clr_brick($b1);
+                       $b1->[2]--; $b1->[5]--;
+                       set_brick($b1);
+                       # say "fallen  $bi1 (@$b1)";
+                       $fallen++;
+                       $f{$bi1}++;
+               }
+               last if !$fallen;
+       }
+       # say "falling $bi0 (@{ $bricks[$bi0] }) falls ", join(',',sort keys %f);
+       $sum += keys %f;
+}
+
+say $sum;