From 2f3400900f836b8b0b781bc3b0c9a380dd999b6d Mon Sep 17 00:00:00 2001
From: "Jan \"Yenya\" Kasprzak" <kas@fi.muni.cz>
Date: Sun, 24 Dec 2023 09:21:23 +0100
Subject: [PATCH] Day 24: Maple

---
 2023/47.pl | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2023/48.pl | 23 +++++++++++++++++++++++
 2 files changed, 75 insertions(+)
 create mode 100755 2023/47.pl
 create mode 100755 2023/48.pl

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;
diff --git a/2023/48.pl b/2023/48.pl
new file mode 100755
index 0000000..89bd982
--- /dev/null
+++ b/2023/48.pl
@@ -0,0 +1,23 @@
+#!/usr/bin/perl -w
+
+use v5.38;
+
+my @stones = map { chomp; [ /-?\d+/g ] } <>;
+
+my @eq;
+for my $stone (0 .. 2) {
+	my @st = @{ $stones[$stone] };
+	for my $co (0 .. 2) {
+		my $c = $st[$co+3];
+		my $d = $st[$co];
+		push @eq, "a$co * t$stone + b$co = $c*t$stone + $d";
+	}
+}
+my @vars;
+push @vars, "a$_", "b$_", "t$_" for 0 .. 2;
+
+# Maple:
+say "res := solve({\n\t", join(",\n\t", @eq), "\n},";
+say "\t[", join(", ", @vars), " ]";
+say ");";
+say "res[1][2]+res[1][5]+res[1][8];";
-- 
2.43.0