From bdd35a7bee7f23c912d0c453abc263805d8d8ccf Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Fri, 7 Nov 2025 12:04:46 +0100
Subject: aoc 2017, days 21-25

---
 2017/src/day22.cpp | 158 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 158 insertions(+)
 create mode 100644 2017/src/day22.cpp

(limited to '2017/src/day22.cpp')

diff --git a/2017/src/day22.cpp b/2017/src/day22.cpp
new file mode 100644
index 0000000..2567fb1
--- /dev/null
+++ b/2017/src/day22.cpp
@@ -0,0 +1,158 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <set>
+#include <string>
+#include <tuple>
+
+using namespace std;
+
+namespace {
+
+set<tuple<int, int>>
+read_file(const filesystem::path& filename)
+{
+	ifstream             file{ filename };
+	set<tuple<int, int>> data;
+
+	int row = 0;
+	for ( string line; getline(file, line); ) {
+		int col = 0;
+
+		for ( char chr: line ) {
+			if ( chr == '#' ) {
+				data.emplace(col, row);
+			}
+			++col;
+		}
+
+		++row;
+	}
+
+	return data;
+}
+
+#if 0
+void
+print(const set<tuple<int, int>>& grid, tuple<int, int> pos)
+{
+	for ( int y = -5; y < 5; ++y ) {
+		for ( int x = -5; x < 5; ++x ) {
+			auto coord = make_tuple(x, y);
+
+			if ( pos == coord ) {
+				cout << '[';
+			}
+			else {
+				cout << ' ';
+			}
+
+			auto chr = grid.contains(coord) ? '#' : '.';
+			cout << chr;
+
+			if ( pos == coord ) {
+				cout << ']';
+			}
+			else {
+				cout << ' ';
+			}
+		}
+		cout << '\n';
+	}
+	cout << '\n';
+}
+#endif
+
+void
+part1(set<tuple<int, int>> grid, tuple<int, int> pos)
+{
+	const array<tuple<int, int>, 4> dirs{
+		make_tuple(-1, 0),
+		make_tuple(0, -1),
+		make_tuple(1, 0),
+		make_tuple(0, 1)
+	};
+	unsigned dir = 1; // up
+
+	int infections = 0;
+	for ( int i = 0; i != 10000; ++i ) {
+		if ( grid.contains(pos) ) {
+			dir = (dir + 1) % 4;
+			grid.erase(pos);
+		}
+		else {
+			dir = (dir + 3) % 4;
+			grid.insert(pos);
+			++infections;
+		}
+
+		auto [dx, dy] = dirs.at(dir);
+		get<0>(pos) += dx;
+		get<1>(pos) += dy;
+	}
+	cout << "Part1: " << infections << '\n';
+}
+
+void
+part2(set<tuple<int, int>> grid, tuple<int, int> pos)
+{
+	const array<tuple<int, int>, 4> dirs{
+		make_tuple(-1, 0),
+		make_tuple(0, -1),
+		make_tuple(1, 0),
+		make_tuple(0, 1)
+	};
+	unsigned dir = 1; // up
+
+	static const int weak     = 0;
+	static const int infected = 1;
+	static const int flagged  = 2;
+
+	map<tuple<int, int>, int> grid_;
+	for ( const auto& value: grid ) {
+		grid_[value] = infected;
+	}
+
+	int infections = 0;
+	for ( int i = 0; i != 10000000; ++i ) {
+		if ( !grid_.contains(pos) ) {
+			grid_[pos] = weak;
+			dir        = (dir + 3) % 4;
+		}
+		else {
+			switch ( grid_[pos] ) {
+			case weak:
+				grid_[pos] = infected;
+				++infections;
+				break;
+			case infected:
+				grid_[pos] = flagged;
+				dir        = (dir + 1) % 4;
+				break;
+			case flagged:
+				grid_.erase(pos);
+				dir = (dir + 2) % 4;
+				break;
+			default:
+				cerr << "Wrong state!!" << '\n';
+				return;
+			}
+		}
+
+		auto [dx, dy] = dirs.at(dir);
+		get<0>(pos) += dx;
+		get<1>(pos) += dy;
+	}
+	cout << "Part2: " << infections << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+	auto grid = read_file("data/day22.txt");
+	part1(grid, { 12, 12 });
+	part2(grid, { 12, 12 });
+}
-- 
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