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/day19.cpp | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 2017/src/day19.cpp

(limited to '2017/src/day19.cpp')

diff --git a/2017/src/day19.cpp b/2017/src/day19.cpp
new file mode 100644
index 0000000..470bb4f
--- /dev/null
+++ b/2017/src/day19.cpp
@@ -0,0 +1,97 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <string>
+#include <tuple>
+
+using namespace std;
+
+namespace {
+
+using dir_type    = tuple<size_t, size_t>;
+using pos_type    = tuple<size_t, size_t>;
+using puzzle_type = map<pos_type, char>;
+
+puzzle_type
+read_file(const filesystem::path& filename)
+{
+	ifstream    file{ filename };
+	puzzle_type data;
+
+	size_t row = 0;
+	for ( string line; getline(file, line); ) {
+		for ( size_t col = 0; col != line.size(); ++col ) {
+			if ( line.at(col) != ' ' ) {
+				data.emplace(pos_type{ col, row }, line.at(col));
+			}
+		}
+		++row;
+	}
+
+	return data;
+}
+
+pos_type
+find_start(const puzzle_type& puzzle)
+{
+	for ( size_t col = 0;; ++col ) {
+		const pos_type pos{ col, 0 };
+		if ( puzzle.contains(pos) && puzzle.at(pos) == '|' ) {
+			return pos;
+		}
+	}
+}
+
+void
+solve(const puzzle_type& puzzle)
+{
+	string result;
+	size_t steps = 0;
+
+	pos_type pos = find_start(puzzle);
+	dir_type dir{ 0, 1 };
+
+	while ( puzzle.contains(pos) ) {
+		auto chr = puzzle.at(pos);
+
+		if ( chr >= 'A' && chr <= 'Z' ) {
+			result += chr;
+		}
+		else if ( chr == '+' ) {
+			auto [dx, dy] = dir;
+			auto left     = dir_type{ -dy, dx };
+			auto right    = dir_type{ dy, -dx };
+
+			pos_type next_left  = { get<0>(pos) + get<0>(left), get<1>(pos) + get<1>(left) };
+			pos_type next_right = { get<0>(pos) + get<0>(right), get<1>(pos) + get<1>(right) };
+
+			if ( puzzle.contains(next_left) ) {
+				dir = left;
+			}
+			else if ( puzzle.contains(next_right) ) {
+				dir = right;
+			}
+			else {
+				cerr << "Error!\n";
+				return;
+			}
+		}
+
+		get<0>(pos) += get<0>(dir);
+		get<1>(pos) += get<1>(dir);
+		++steps;
+	}
+
+	cout << "Part1: " << result << '\n';
+	cout << "Part2: " << steps << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+	auto puzzle = read_file("data/day19.txt");
+	solve(puzzle);
+}
-- 
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