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/day18.cpp | 266 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 266 insertions(+)
 create mode 100644 2017/src/day18.cpp

(limited to '2017/src/day18.cpp')

diff --git a/2017/src/day18.cpp b/2017/src/day18.cpp
new file mode 100644
index 0000000..bfdd7e3
--- /dev/null
+++ b/2017/src/day18.cpp
@@ -0,0 +1,266 @@
+#include <charconv>
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <queue>
+#include <sstream>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+template<typename T>
+struct CPU {
+	[[nodiscard]]
+	T get(const string& ref)
+	{
+		T value{};
+		auto [ptr, ec] = from_chars(ref.data(), ref.data() + ref.size(), value);
+
+		if ( ec == errc() ) {
+			return value;
+		}
+
+		return memory[ref];
+	}
+
+	void set(const string& ref, T value)
+	{
+		memory[ref] = value;
+	}
+
+	void add(const string& ref, T value)
+	{
+		memory[ref] += value;
+	}
+
+	void mul(const string& ref, T value)
+	{
+		memory[ref] *= value;
+	}
+
+	void mod(const string& ref, T value)
+	{
+		memory[ref] %= value;
+	}
+
+	T execute(const vector<vector<string>>& code)
+	{
+		long played_sound{};
+
+		for ( size_t ip = 0; ip < code.size(); ++ip ) {
+			const auto& line   = code.at(ip);
+			const auto& opcode = line.at(0);
+
+			if ( opcode == "snd" ) {
+				played_sound = get(line.at(1));
+			}
+			else if ( opcode == "rcv" ) {
+				auto value = get(line.at(1));
+				if ( value != 0 ) {
+					return played_sound;
+				}
+			}
+			else if ( opcode == "set" ) {
+				set(line.at(1), get(line.at(2)));
+			}
+			else if ( opcode == "add" ) {
+				add(line.at(1), get(line.at(2)));
+			}
+			else if ( opcode == "mul" ) {
+				mul(line.at(1), get(line.at(2)));
+			}
+			else if ( opcode == "mod" ) {
+				mod(line.at(1), get(line.at(2)));
+			}
+			else if ( opcode == "jgz" ) {
+				auto value = get(line.at(1));
+				if ( value > 0 ) {
+					auto offset = get(line.at(2));
+					ip += static_cast<size_t>(offset - 1);
+				}
+			}
+			else {
+				cerr << "unknown opcode: " << opcode << '\n';
+				return -1;
+			}
+		}
+		return -1;
+	}
+
+	map<string, T> memory;
+};
+
+template<typename T>
+struct CPU2 {
+	CPU2(queue<T>& in, queue<T>& out)
+	    : in{ in }
+	    , out{ out }
+	{
+	}
+
+	[[nodiscard]]
+	T get(const string& ref)
+	{
+		T value{};
+		auto [ptr, ec] = from_chars(ref.data(), ref.data() + ref.size(), value);
+
+		if ( ec == errc() ) {
+			return value;
+		}
+
+		return memory[ref];
+	}
+
+	void set(const string& ref, T value)
+	{
+		memory[ref] = value;
+	}
+
+	void add(const string& ref, T value)
+	{
+		memory[ref] += value;
+	}
+
+	void mul(const string& ref, T value)
+	{
+		memory[ref] *= value;
+	}
+
+	void mod(const string& ref, T value)
+	{
+		memory[ref] %= value;
+	}
+
+	bool step(const vector<vector<string>>& code)
+	{
+		if ( ip >= code.size() ) {
+			return false;
+		}
+
+		const auto& line   = code.at(ip);
+		const auto& opcode = line.at(0);
+
+		if ( opcode == "snd" ) {
+			out.push(get(line.at(1)));
+			++send_count;
+		}
+		else if ( opcode == "rcv" ) {
+			if ( in.empty() ) {
+				waiting = true;
+				return true;
+			}
+			else {
+				auto value = in.front();
+				in.pop();
+				set(line.at(1), value);
+				waiting = false;
+			}
+		}
+		else if ( opcode == "set" ) {
+			set(line.at(1), get(line.at(2)));
+		}
+		else if ( opcode == "add" ) {
+			add(line.at(1), get(line.at(2)));
+		}
+		else if ( opcode == "mul" ) {
+			mul(line.at(1), get(line.at(2)));
+		}
+		else if ( opcode == "mod" ) {
+			mod(line.at(1), get(line.at(2)));
+		}
+		else if ( opcode == "jgz" ) {
+			auto value = get(line.at(1));
+			if ( value > 0 ) {
+				auto offset = get(line.at(2));
+				ip += static_cast<size_t>(offset);
+				return true;
+			}
+		}
+		else {
+			cerr << "unknown opcode: " << opcode << '\n';
+			return false;
+		}
+
+		++ip;
+
+		return true;
+	}
+
+	size_t         ip{};
+	queue<T>&      in;
+	queue<T>&      out;
+	bool           waiting{ false };
+	T              send_count{};
+	map<string, T> memory;
+};
+
+vector<string>
+split(const string& line)
+{
+	stringstream   strm{ line };
+	vector<string> data;
+
+	for ( string line; strm >> line; ) {
+		data.emplace_back(line);
+	}
+
+	return data;
+}
+
+vector<vector<string>>
+read_file(const filesystem::path& filename)
+{
+	ifstream               file{ filename };
+	vector<vector<string>> data;
+
+	for ( string line; getline(file, line); ) {
+		const auto parts = split(line);
+		data.emplace_back(parts);
+	}
+
+	return data;
+}
+
+void
+part1(const vector<vector<string>>& code)
+{
+	CPU<long> cpu{};
+
+	cout << "Part1: " << cpu.execute(code) << '\n';
+}
+
+void
+part2(const vector<vector<string>>& code)
+{
+	queue<long> queue1;
+	queue<long> queue2;
+	CPU2<long>  cpu1{ queue1, queue2 };
+	CPU2<long>  cpu2{ queue2, queue1 };
+
+	cpu1.set("p", 0);
+	cpu2.set("p", 1);
+
+	for ( ;; ) {
+		auto cpu1_running = cpu1.step(code);
+		auto cpu2_running = cpu2.step(code);
+
+		if ( (cpu1.waiting || !cpu1_running) && (cpu2.waiting || !cpu2_running) ) {
+			break;
+		}
+	}
+	cout << "Part2: " << cpu2.send_count << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+	auto instr = read_file("data/day18.txt");
+	part1(instr);
+	part2(instr);
+}
-- 
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