From ab08f90e568538823f4c150df9b6641849b78123 Mon Sep 17 00:00:00 2001
From: "Jan \"Yenya\" Kasprzak" <kas@fi.muni.cz>
Date: Sat, 18 Dec 2021 18:18:30 +0100
Subject: [PATCH] Day 18: slightly cleaner solution

---
 36.pl | 79 +++++++++++++++++++++++++----------------------------------
 1 file changed, 34 insertions(+), 45 deletions(-)

diff --git a/36.pl b/36.pl
index 4371f37..3047f40 100755
--- a/36.pl
+++ b/36.pl
@@ -2,57 +2,46 @@
 
 use v5.16;
 
-$/ = undef;
-my @nums = split /\n/, <>;
+sub add {
+	$_ = "[$_[0],$_[1]]";
+	my $modified;
+	do {
+		$modified = undef;
+		my ($i, $depth) = (0, 0);
+		while ($i < length) {
+			$depth-- if substr($_, $i, 1) eq ']';
+			$depth++ if substr($_, $i, 1) eq '[';
+			
+			if ($depth >= 5) {
+				pos = $i;
+				next unless s/\G\[(\d+),(\d+)\]/X/;
+				my ($l, $r) = ($1, $2);
+				s/(\d+)([^\d]*X)/($1+$l).$2/e;
+				s/(X[^\d]*)(\d+)/$1.($2+$r)/e;
+				s/X/0/;
+				$modified++; $depth--;
+			}
+			$i++;
+		}
+		$modified++ if s|\d{2,}|'['.int($&/2).','.int(($&+1)/2).']'|e;
+	} while ($modified);
+	return $_;
+}
+
+sub magnitude { $_ = shift; 1 while s/\[(\d+),(\d+)\]/3*$1+2*$2/e; $_ }
+
+use List::Util qw(reduce);
+
+chomp (my @nums = <>);
+
+say magnitude( reduce { add($a, $b) } @nums );
 
 my $max = 0;
 for my $i (0 .. $#nums) {
 for my $j (0 .. $#nums) {
 	next if $i == $j;
-	my $r = add($nums[$i], $nums[$j]);
+	my $r = magnitude( add($nums[$i], $nums[$j]) );
 	$max = $r if ($max < $r);
 } }
 
 say $max;
-
-sub add {
-	my ($n1, $n2) = @_;
-	say "\nadd:   $n1\nto:    $n2";
-	my $res = "[$n1,$n2]";
-	ACTION:
-	while (1) {
-		say "have:  $res";
-		# explode
-		my $depth = 0;
-		for my $i (0 .. length($res)-1) {
-			$depth++ if substr($res, $i, 1) eq '[';
-			$depth-- if substr($res, $i, 1) eq ']';
-			
-			if ($depth >= 5) {
-				pos($res) = $i;
-				next if $res !~ /\G\[(\d+),(\d+)\]/;
-				say "explode at $i";
-				pos($res) = $i;
-				$res =~ s/\G\[(\d+),(\d+)\]/X/;
-				say "X:     $res";
-				my $l = $1;
-				my $r = $2;
-				$res =~ s/(\d+)([^\d]*X)/($1+$l).$2/e;
-				$res =~ s/(X[^\d]*)(\d+)/"$1".($2+$r)/e;
-				$res =~ s/X/0/;
-				say "after: $res";
-				next ACTION;
-			}
-		}
-		# split
-		if ($res =~ s|\d{2,}|'['.int($&/2).','.int(($&+1)/2).']'|e) {
-			say "split: $res";
-			next ACTION;
-		}
-		last;
-	}
-	1 while $res =~ s/\[(\d+),(\d+)\]/3*$1+2*$2/e;
-	return $res;
-}
-
-
-- 
2.43.0