Moved 2021 to a subdir

[aoc.git] / 2021 / 25.pl

diff --git a/2021/25.pl b/2021/25.pl
new file mode 100755 (executable)
index 0000000..ceeb16f
--- /dev/null
+++ b/2021/25.pl
@@ -0,0 +1,38 @@
+#!/usr/bin/perl -w
+
+use v5.16;
+
+my %dots;
+
+while (<>) {
+       chomp;
+       my ($x, $y) = split /,/;
+       last if !defined $y;
+       $dots{$x}{$y}++;
+}
+
+my ($maxx, $maxy);
+while (<>) {
+       chomp;
+       my ($axis, $val) = /fold along (.)=(\d+)/;
+
+       for my $x (keys %dots) {
+       for my $y (keys %{$dots{$x}}) {
+               if ($axis eq 'x' && $x > $val) {
+                       $dots{2*$val - $x}{$y}++;
+                       delete $dots{$x}{$y};
+               } elsif ($axis eq 'y' && $y > $val) {
+                       $dots{$x}{2*$val - $y}++;
+                       delete $dots{$x}{$y};
+               }
+       } }
+       last;
+}
+
+my $sum;
+for my $x (keys %dots) {
+       $sum += keys %{$dots{$x}};
+}
+
+say $sum;
+