First half of Year 2019

[aoc.git] / 2019 / 19.pl

diff --git a/2019/19.pl b/2019/19.pl
new file mode 100755 (executable)
index 0000000..8755717
--- /dev/null
+++ b/2019/19.pl
@@ -0,0 +1,73 @@
+#!/usr/bin/perl -w
+
+use v5.16;
+
+my %m;
+$; = ',';
+my $y = 0;
+my ($maxx, $maxy);
+while (<>) {
+       chomp;
+       my $x = 0;
+       $maxx = length;
+       for my $c (split //) {
+               $m{$x,$y}++ if $c eq '#';
+               $x++;
+       }
+       $y++;
+}
+$maxy = $y;
+
+my %gcd;
+sub gcd {
+       my ($n1, $n2) = @_;
+       return $gcd{$n1,$n2} //=
+               $n1 == $n2 ? $n1
+               : $n1 > $n2 ? gcd($n2, $n1-$n2)
+               : gcd($n1, $n2-$n1);
+}
+
+my %dir;
+sub dir1 {
+       my ($x, $y) = @_;
+       return (0, 1) if $x == 0 && $y > 0;
+       return (0,-1) if $x == 0 && $y < 0;
+       return (1, 0) if $y == 0 && $x > 0;
+       return (-1,0) if $y == 0 && $x < 0;
+       my $g = gcd(abs($x), abs($y));
+       return ($x/$g, $y/$g);
+}
+
+sub dir {
+       my ($x, $y) = @_;
+       $dir{$x,$y} //= [ dir1($x,$y) ];
+       return @{ $dir{$x,$y} };
+}
+
+my %sum;
+for (keys %m) {
+       my ($x,$y) = split /,/;
+       ASTEROID:
+       for (keys %m) {
+               my ($ax, $ay) = split /,/;
+               next if $ax == $x && $ay == $y;
+               say "testing $ax,$ay from $x,$y";
+               my ($dx, $dy) = dir($ax-$x, $ay-$y);
+               # next if $tried_dir{$dx,$dy}++;
+               say "dx,dy=$dx,$dy";
+               my ($x0, $y0) = ($x+$dx, $y+$dy);
+               while ($x0 != $ax || $y0 != $ay) {
+                       say "x0,y0=$x0,$y0";
+                       if ($m{$x0,$y0}) {
+                               say "$ax,$ay cannot be seen from $x,$y because of $x0,$y0";
+                               next ASTEROID;
+                       }
+                       $x0 += $dx; $y0 += $dy;
+               }
+               say "$ax,$ay CAN be seen from $x,$y";
+               $sum{$x,$y}++;
+       }
+}
+
+my @s = sort { $sum{$b} <=> $sum{$a} } keys %sum;
+say $s[0], '=', $sum{$s[0]};