From effe859821bf2efb6064b8adc70d520dd02bdcb6 Mon Sep 17 00:00:00 2001
From: "Jan \"Yenya\" Kasprzak" <kas@fi.muni.cz>
Date: Sun, 10 Dec 2023 16:28:10 +0100
Subject: [PATCH] Day 10: polished solution

---
 2023/20.pl | 123 +++++++++++++++++++++--------------------------------
 1 file changed, 48 insertions(+), 75 deletions(-)

diff --git a/2023/20.pl b/2023/20.pl
index c6d299a..9a359f5 100755
--- a/2023/20.pl
+++ b/2023/20.pl
@@ -1,101 +1,74 @@
 #!/usr/bin/perl -w
 
 use v5.38;
-use experimental 'multidimensional', 'for_list', 'builtin';
-use builtin 'indexed';
-use List::Util;
-use Y::AoC::Task;
+use experimental 'multidimensional';
 $; = ';';
-# t;
 
-my @map = map { chomp; [ split //, ".$_." ] } <>;
-push @map, [ ('.') x @{ $map[0]} ];
-unshift @map, [ ('.') x @{$map[0]} ];
-my $xmax = $#{$map[0]};
-my $ymax = $#map;
+my @map;
+my ($x, $y);
 
-my ($sx, $sy);
-for my $x (0 .. $xmax) {
-for my $y (0 .. $ymax) {
-	next if $map[$y][$x] ne 'S';
-	$sx = $x; $sy = $y;
-} }
+while (<>) {
+	chomp;
+	if (/S/g) {
+		$x = pos;
+		$y = 1 + @map;
+	}
+	push @map, [ split //, ".$_." ];
+}
+
+push    @map, [ ('.') x @{ $map[0] } ];
+unshift @map, [ ('.') x @{ $map[0] } ];
 
+my $xmax = $#{$map[0]};
+my $ymax = $#map;
 
+# 0=E 1=S 2=W 3=N
 my %dirs = (
-	'|' => [ 0, -1,  0,  1],
-	'-' => [-1,  0,  1,  0],
-	'J' => [-1,  0,  0, -1],
-	'L' => [ 1,  0,  0, -1],
-	'F' => [ 1,  0,  0,  1],
-	'7' => [-1,  0,  0,  1],
+	'|' => '13',
+	'-' => '02',
+	'J' => '23',
+	'L' => '03',
+	'F' => '01',
+	'7' => '12',
 );
+my @dx = (1, 0, -1, 0);
+my @dy = (0, 1, 0, -1);
 
-
-if ($map[$sy][$sx-1] eq '-' && $map[$sy][$sx+1] eq '-') {
-	$map[$sy][$sx] = '-';
-} elsif ($map[$sy+1][$sx] eq '|' && $map[$sy-1][$sx] eq '|') {
-	$map[$sy][$sx] = '|';
-} elsif ($map[$sy][$sx-1] eq '-' && $map[$sy-1][$sx] eq '|') {
-	$map[$sy][$sx] = 'J';
-} elsif ($map[$sy][$sx-1] eq '-' && $map[$sy+1][$sx] eq '|') {
-	$map[$sy][$sx] = '7';
-} elsif ($map[$sy][$sx+1] eq '-' && $map[$sy-1][$sx] eq '|') {
-	$map[$sy][$sx] = 'L';
-} elsif ($map[$sy][$sx+1] eq '-' && $map[$sy+1][$sx] eq '|') {
-	$map[$sy][$sx] = 'F';
+my $dir;
+for my $d (0 .. 3) {
+	my $revdir = $d ^ 2;
+	my $p = $map[ $y+$dy[$d] ][ $x+$dx[$d] ];
+	$dir .= $d if $dirs{$p} =~ /$revdir/;
 }
 
-say "starting at $sx, $sy $map[$sy][$sx]";
+my %dir2sym = reverse %dirs;
+$map[$y][$x] = $dir2sym{$dir}; # fill in the start point
+$dir =~ s/.//; # Take any valid direction
+
 my %seen;
-my $len = 0;
-my ($px, $py);
-while (!$seen{$sx,$sy}++) {
-	my @d = $dirs{ $map[$sy][$sx] }->@*;
-	if (!defined($px) || ($px != $d[0] || $py != $d[1])) {
-		$sx += $d[0];
-		$sy += $d[1];
-		$px = -$d[0];
-		$py = -$d[1];
-	} else {
-		$sx += $d[2];
-		$sy += $d[3];
-		$px = -$d[2];
-		$py = -$d[3];
-	}
-	++$len;
+while (1) {
+	$x += $dx[$dir];
+	$y += $dy[$dir];
+	last if $seen{$x,$y}++;
+	$dir ^= 2;
+	($dir) = $dirs{ $map[$y][$x] } =~ /([^$dir])/;
 }
 
-say "loop len ", $len/2;
+say "loop half: ", (keys %seen)/2;
 
 my $sum;
-for my $x (0 .. $xmax) {
+for my $y (0 .. $ymax) {
 	my $in = 0;
-	my $left = 0;
-	for my $y (0 .. $ymax) {
+	for my $x (0 .. $xmax) {
 		if ($seen{$x,$y}) {
 			my $pt = $map[$y][$x];
-			if ($pt eq '-') {
-				$in = !$in;
-			} elsif ($pt eq '7') {
-				$left = 1;
-			} elsif ($pt eq 'F') {
-				$left = -1;
-			} elsif ($pt eq 'J') {
-				if ($left == -1) {
-					$in = !$in;
-				}
-			} elsif ($pt eq 'L') {
-				if ($left == 1) {
-					$in = !$in;
-				}
-			}
-			say "$x $y in $in left $left";
-		} elsif ($in) {
-			say "$x $y inside";
+			$in += 2 if $pt eq '|';
+			$in++    if $pt =~ /[L7]/;
+			$in--    if $pt =~ /[FJ]/;
+		} elsif ($in % 4 == 2) {
 			$sum++;
 		}
 	}
 }
 
-say $sum;
+say "inside: ", $sum;
-- 
2.43.5