Day 19. "practical soultion"

[aoc2020.git] / 37.pl

diff --git a/37.pl b/37.pl
new file mode 100755 (executable)
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--- /dev/null
+++ b/37.pl
@@ -0,0 +1,49 @@
+#!/usr/bin/perl -w
+
+use strict;
+
+my %rules;
+my %subrules;
+my %final;
+
+while (<>) {
+       chomp;
+       last if /^$/;
+       my ($id, $rest) = /\A(\d+): (.*)\z/;
+       if ($rest =~ /"(.)"/) {
+               $final{$id} = $1;
+               next;
+       }
+       my @alts;
+       my @subalts;
+       for my $seq (split /\|/, $rest) {
+               push @alts, [ $seq =~ /(\d+)/g ];
+               push @subalts, ($seq =~ /(\d+)/g);
+       }
+       $rules{$id} = \@alts;
+       $subrules{$id} = \@subalts;
+}
+
+while (keys %rules) {
+       RULE:
+       for my $id (keys %rules) {
+               for my $subr (@{ $subrules{$id} }) {
+                       next RULE if !defined $final{$subr};
+               }
+               $final{$id} = '(?:(?:' . join(')|(?:', map {
+                       join('', map { $final{$_} } @$_)
+                       } @{ $rules{$id} }) .'))';
+               print "\$final{$id} = $final{$id}\n";
+               delete $rules{$id};
+       }
+}
+
+my $re = '\A'.$final{0}.'\z';
+
+my $count = 0;
+while (<>) {
+       chomp;
+       $count++ if ($_ =~ /$re/);
+}
+
+print "$count matched\n";