Day 14: too slow. And no regexes :-(

[aoc2021.git] / 28.pl

diff --git a/28.pl b/28.pl
new file mode 100755 (executable)
index 0000000..5717759
--- /dev/null
+++ b/28.pl
@@ -0,0 +1,41 @@
+#!/usr/bin/perl -w
+
+use v5.16;
+use List::Util qw(sum0);
+
+chomp (my $tmpl = <>);
+scalar <>;
+
+my (%r1, %r2, %ins);
+while (<>) {
+       chomp;
+       my ($s1, $s2, $d) = /([A-Z])/g;
+       $r1{"$s1$s2"} = "$s1$d";
+       $r2{"$s1$s2"} = "$d$s2";
+       $ins{"$s1$s2"} = $d;
+}
+
+my %count;
+my %p;
+for my $i (0 .. length($tmpl) - 2) {
+       $p{substr($tmpl, $i, 2)}++;
+       $count{substr($tmpl, $i, 1)}++;
+}
+$count{substr($tmpl, -1, 1)}++;
+
+for (1 .. 40) {
+       my %p1;
+       for my $pair (keys %p) {
+               if ($r1{$pair}) {
+                       $p1{$r1{$pair}} += $p{$pair};
+                       $p1{$r2{$pair}} += $p{$pair};
+                       $count{$ins{$pair}} += $p{$pair};
+               }
+       }
+       %p = %p1;
+}
+
+my @count = sort { $a <=> $b } values %count;
+
+say $count[-1] - $count[0];
+