The rest of Year 2017

[aoc.git] / 2017 / 32.pl

diff --git a/2017/32.pl b/2017/32.pl
new file mode 100755 (executable)
index 0000000..61d30dd
--- /dev/null
+++ b/2017/32.pl
@@ -0,0 +1,47 @@
+#!/usr/bin/perl
+
+use v5.30;
+use strict;
+
+my $row = join('', 'a' .. 'p');
+# my $row = join('', 'a' .. 'e');
+
+chomp (my $dance = <>);
+my @dance = split /,/, $dance;
+
+sub do_dance {
+       for my $move (@dance) {
+               chomp $move;
+               if ($move =~ /s(\d+)/) {
+                       $row =~ s/(.*)(.{$1})/\2\1/;
+               } elsif ($move =~ /x(\d+)\/(\d+)/) {
+                       my ($a, $b) = (substr($row, $1, 1), substr($row, $2, 1));
+                       substr($row, $1, 1) = $b;
+                       substr($row, $2, 1) = $a;
+               } elsif ($move =~ /p(\w)\/(\w)/) {
+                       eval "\$row =~ y/$1$2/$2$1/";
+               }
+       }
+}
+
+my %seen;
+my $i = 0;
+while (1) {
+       if ($seen{$row}) {
+               last;
+       } else {
+               $seen{$row} = $i;
+       }
+       do_dance();
+       $i++;
+}
+
+my $period = $i - $seen{$row};
+say "period $period from $seen{$row} to $i";
+
+my $count = 1_000_000_000 - $seen{$row};
+$count %= $period;
+do_dance() while $count--;
+
+say $row;
+