X-Git-Url: https://www.fi.muni.cz/~kas/git//home/kas/public_html/git/?a=blobdiff_plain;f=2023%2F47.pl;fp=2023%2F47.pl;h=4a96dfae9f1c15109f0faa8a0fea55c8da292af1;hb=2f3400900f836b8b0b781bc3b0c9a380dd999b6d;hp=0000000000000000000000000000000000000000;hpb=cb7662a16eca1ff55e28338ef8ea7161224ac078;p=aoc.git

diff --git a/2023/47.pl b/2023/47.pl
new file mode 100755
index 0000000..4a96dfa
--- /dev/null
+++ b/2023/47.pl
@@ -0,0 +1,52 @@
+#!/usr/bin/perl -w
+
+use v5.38;
+
+my @stones = map { chomp; [ /-?\d+/g ] } <>;
+my ($min, $max) = (200000000000000, 400000000000000);
+# my ($min, $max) = (7, 27);
+
+sub from_param {
+	my ($x0, $y0, $z0, $xs, $ys, $zs) = @_;
+	return ($ys/$xs, $y0-($ys*$x0/$xs));
+}
+
+sub to_time {
+	my ($x, $xs, $x0) = @_;
+	return ($x-$x0)/$xs;
+}
+
+my $sum;
+for my $s1 (0 .. $#stones-1) {
+	my @st1 = @{ $stones[$s1] };
+	my ($a, $b) = from_param(@st1);
+	say "y=$a*x + $b";
+
+	for my $s2 ($s1+1 .. $#stones) {
+		my @st2 = @{ $stones[$s2] };
+		my ($c, $d) = from_param(@st2);
+		say "  y=$c*x + $d";
+		if ($a == $c) {
+			if ($b == $d) {
+				die "two same lines";
+			}
+			next;
+		}
+		my $xi = ($d-$b)/($a-$c);
+		my $yi = $a*$xi + $b;
+		my $t0 = to_time($xi, $st1[3], $st1[0]);
+		my $t1 = to_time($xi, $st2[3], $st2[0]);
+		say "  intersection at $xi, $yi at $t0 $t1";
+		if ($xi < $min || $xi > $max || $yi < $min || $yi > $max) {
+			say "  outside";
+			next;
+		}
+		if ($t0 < 0 || $t1 < 0) {
+			say "  in the past";
+			next;
+		}
+		$sum++;
+	}
+}
+
+say $sum;