From adc51097b896f6cc3a89391ce272b4798aa42a51 Mon Sep 17 00:00:00 2001
From: "Jan \"Yenya\" Kasprzak" <kas@fi.muni.cz>
Date: Thu, 14 Dec 2023 17:45:51 +0100
Subject: [PATCH] Day 14 part 2: pure regex-based solution

---
 2023/28.pl | 52 ++++++++++++++--------------------------------------
 1 file changed, 14 insertions(+), 38 deletions(-)

diff --git a/2023/28.pl b/2023/28.pl
index 0699eb4..2d147f4 100755
--- a/2023/28.pl
+++ b/2023/28.pl
@@ -2,48 +2,24 @@
 
 use v5.38;
 
-my @map = map { chomp; [ split // ] } <>;
-my $xmax = $#{ $map[0] };
-my $ymax = $#map;
-
-my %seen;
-my @score;
-my $round;
-my $key;
+my $map; { local $/; $map = <>; }
 
+my (@score, %seen, $round);
 while (++$round) {
 	for (1 .. 4) {
-		for my $y (0 .. $ymax) {
-			for my $x (0 .. $xmax) {
-				next if $map[$y][$x] ne 'O';
-				my $y1 = $y;
-				while ($y1 && $map[$y1-1][$x] eq '.') {
-					$map[$y1][$x] = '.';
-					$map[--$y1][$x] = 'O';
-				}
-			}
-		}
-
-		@map = map { # rotate clockwise
-			my $x = $_;
-			[ map { $map[$_][$x] } reverse 0 .. $ymax ]
-		} 0 .. $xmax;
-		($xmax, $ymax) = ($ymax, $xmax);
-	}
-
-	$key = join("\n", map { join('', @$_) } @map);
-	last if $seen{$key};
-
-	my $sum = 0;
-	for my $y (0 .. $ymax) {
-		for my $x (0 .. $xmax) {
-			$sum += $ymax + 1 - $y if $map[$y][$x] eq 'O';
-		}
+		my $map1;
+		do { # rotate the map:
+			$map1 .= join('', reverse $map =~ /^./gm) . "\n"
+		} while $map =~ s/^.//gm;
+		chomp ($map = $map1);
+		1 while $map =~ s/O(\.+)/$1O/g; # move O's to the right
 	}
+	$score[$round] +=()= substr($map, pos($map)) =~ /\n/g
+		while $map =~ /O/g;
 
-	$seen{$key} = $round;
-	$score[$round] = $sum;
+	last if $seen{$map};
+	$seen{$map} = $round;
 }
 
-my $remains = (1000000000 - $round) % ($round - $seen{$key});
-say $score[$seen{$key} + $remains];
+my $remains = (1000000000 - $round) % ($round - $seen{$map});
+say $score[$seen{$map} + $remains];
-- 
2.43.0