From 756f22d58bb198b8f34589c112e1003614ccdcd6 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 2 Nov 2025 21:41:58 +0100
Subject: aoc 2017, days 1-20

---
 2017/src/day13.cpp | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 2017/src/day13.cpp

(limited to '2017/src/day13.cpp')

diff --git a/2017/src/day13.cpp b/2017/src/day13.cpp
new file mode 100644
index 0000000..759f302
--- /dev/null
+++ b/2017/src/day13.cpp
@@ -0,0 +1,77 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <tuple>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+vector<tuple<unsigned long, unsigned long>>
+read_file(const filesystem::path& filename)
+{
+	ifstream      file{ filename };
+	unsigned long depth = 0;
+	unsigned long range = 0;
+	char          colon = 0;
+
+	vector<tuple<unsigned long, unsigned long>> data;
+
+	while ( file >> depth >> colon >> range ) {
+		data.emplace_back(depth, range);
+	}
+
+	return data;
+}
+
+template<typename T>
+T
+get_pos(T depth, T range, T time)
+{
+	const auto period    = 2 * (range - 1);
+	const auto remainder = (depth + time) % period;
+	return remainder < range ? remainder : period - remainder;
+}
+
+void
+part1(const vector<tuple<unsigned long, unsigned long>>& data)
+{
+	unsigned long sum = 0;
+	for ( const auto [depth, range]: data ) {
+		if ( get_pos(depth, range, 0UL) == 0 ) {
+			sum += depth * range;
+		}
+	}
+	cout << "Part1: " << sum << '\n';
+}
+
+void
+part2(const vector<tuple<unsigned long, unsigned long>>& data)
+{
+	for ( unsigned long delay = 0;; ++delay ) {
+		bool pass = true;
+
+		for ( const auto [depth, range]: data ) {
+			if ( get_pos(depth, range, delay) == 0 ) {
+				pass = false;
+				break;
+			}
+		}
+
+		if ( pass ) {
+			cout << "Part2: " << delay << '\n';
+			return;
+		}
+	}
+}
+
+} // namespace
+
+int
+main()
+{
+	auto data = read_file("data/day13.txt");
+	part1(data);
+	part2(data);
+}
-- 
cgit v1.3