Year 2018

[aoc.git] / 2018 / 43.pl

diff --git a/2018/43.pl b/2018/43.pl
new file mode 100755 (executable)
index 0000000..21407e0
--- /dev/null
+++ b/2018/43.pl
@@ -0,0 +1,38 @@
+#!/usr/bin/perl -w
+
+use v5.36;
+use strict;
+use feature 'multidimensional';
+
+my $depth = 11739;
+my ($tx, $ty) = (11,718);
+
+my %gi;
+sub gi2el($gi) { ($gi + $depth) % 20183 }
+my %el;
+
+my $sum = 0;
+for my $n (1 .. $tx + $ty) {
+       my $y = 0;
+       my $x = $n;
+       for my $i (0 .. $n) {
+               if (($x == 0 && $y == 0) || ($x == $tx && $y == $ty)) {
+                       $gi{$x,$y} = 0;
+               } elsif ($y == 0) {
+                       $gi{$x,$y} = 16807*$x;
+               } elsif ($x == 0) {
+                       $gi{$x,$y} = 48271*$y;
+               } else {
+                       $gi{$x,$y} = $el{$x-1,$y} * $el{$x,$y-1};
+               }
+               $el{$x,$y} = gi2el($gi{$x,$y});
+               $sum += $el{$x,$y} % 3
+                       if $x <= $tx && $y <= $ty;
+               $y++;
+               $x--;
+       }
+}
+
+say $sum;
+
+