From d9fbaa155185220ee141f75d764890983ef35ca2 Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano@tronto.net>
Date: Sat, 14 Dec 2024 08:38:52 +0100
Subject: Day 14 2024 (I did not like this one)

---
 2024/14/day14b.cpp | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 2024/14/day14b.cpp

(limited to '2024/14/day14b.cpp')

diff --git a/2024/14/day14b.cpp b/2024/14/day14b.cpp
new file mode 100644
index 0000000..2402c0c
--- /dev/null
+++ b/2024/14/day14b.cpp
@@ -0,0 +1,85 @@
+/*
+I ran the simulation at 1FPS for a few minutes, staring at the screen and
+hoping to see a Christmas tree, without luck. But I noticed that the robots
+formed a strange "vertical" pattern every 103 timesteps, starting at t=30,
+and a strange "horizontal" pattern every 101 timesteps, starting at t=81.
+So I solved the diophantine equation 30+103y = 81+101x, and the smallest
+solution (y=76, x=77) gave the correct answer t=30+103*76=7858
+*/
+
+#include <algorithm>
+#include <cstdint>
+#include <iostream>
+#include <map>
+#include <ranges>
+#include <set>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <unistd.h>
+#include <vector>
+using namespace std;
+
+#define N 101
+#define M 103
+#define T 100
+
+char board[N][M];
+
+struct Robot {
+	pair<int64_t, int64_t> p, v;
+	Robot(int64_t p1, int64_t p2, int64_t v1, int64_t v2) : p(p1, p2), v(v1, v2) {}
+};
+
+int quadrant(pair<int64_t, int64_t> p) {
+	if (p.first < N/2 && p.second < M/2)
+		return 1;
+	if (p.first < N/2 && p.second > M/2)
+		return 2;
+	if (p.first > N/2 && p.second < M/2)
+		return 3;
+	if (p.first > N/2 && p.second > M/2)
+		return 4;
+	return 0;
+}
+
+pair<int64_t, int64_t> pos(Robot r, int64_t t) {
+	return make_pair((r.p.first + t*(r.v.first+N))%N,
+	    (r.p.second + t*(r.v.second+M))%M);
+}
+
+void visualize(vector<Robot>& robots, int64_t t) {
+	for (int i = 0; i < N; i++)
+		for (int j = 0; j < M; j++)
+			board[i][j] = ' ';
+	for (const auto& r : robots) {
+		auto [x,y] = pos(r, t);
+		board[x][y] = '*';
+	}
+	for (int i = 0; i < N; i++) {
+		for (int j = 0; j < M; j++)
+			cout << board[i][j];
+		cout << endl;
+	}
+	cout << endl;
+}
+
+int main() {
+	string line;
+	int64_t p1, p2, v1, v2, q[5] = {0};
+	vector<Robot> r;
+	while (cin >> p1 >> p2 >> v1 >> v2)
+		r.push_back(Robot(p1, p2, v1, v2));
+
+
+	/* Starts at the solution */
+	for (int64_t t = 7858; ; t++) {
+		cout << "visualization of time " << t << ": " << endl;
+		sleep(1);
+		visualize(r, t);
+	}
+
+	cout << q[1] * q[2] * q[3] * q[4] << endl;
+
+	return 0;
+}
-- 
cgit v1.3