From ae1e96f10b399266825e275ca4a8100ceede9cad Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Thu, 23 Oct 2025 19:28:20 +0200
Subject: days 19-25, aoc 2016

---
 2016/src/day25.cpp | 210 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 210 insertions(+)
 create mode 100644 2016/src/day25.cpp

(limited to '2016/src/day25.cpp')

diff --git a/2016/src/day25.cpp b/2016/src/day25.cpp
new file mode 100644
index 0000000..ba3ad04
--- /dev/null
+++ b/2016/src/day25.cpp
@@ -0,0 +1,210 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <optional>
+#include <sstream>
+#include <string>
+#include <utility>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+enum class OpCode : uint8_t {
+	CPY,
+	INC,
+	DEC,
+	JNZ,
+	OUT,
+};
+
+using memory_type = map<char, int>;
+
+struct Argument {
+	explicit Argument(string value)
+	    : value{ std::move(value) }
+	{
+	}
+
+	[[nodiscard]]
+	int eval(const memory_type& memory) const
+	{
+		const auto chr = value.at(0);
+
+		if ( chr >= 'a' && chr <= 'z' ) {
+			return memory.at(chr);
+		}
+		else {
+			return stoi(value);
+		}
+	}
+
+	[[nodiscard]]
+	char reg() const
+	{
+		if ( !is_reg() ) {
+			throw runtime_error("invalid register access! "s + value);
+		}
+
+		return value.at(0);
+	}
+
+	[[nodiscard]]
+	bool is_reg() const
+	{
+		const auto chr = value.at(0);
+
+		return chr >= 'a' && chr <= 'z';
+	}
+
+	string value;
+};
+
+struct Instruction {
+	Instruction(OpCode opCode, const Argument& x)
+	    : opCode{ opCode }
+	    , x{ x }
+	{
+	}
+
+	Instruction(OpCode opCode, const Argument& x, const Argument& y)
+	    : opCode{ opCode }
+	    , x{ x }
+	    , y{ y }
+	{
+	}
+
+	OpCode             opCode;
+	optional<Argument> x;
+	optional<Argument> y;
+};
+
+vector<string>
+split_words(const string& line, char sep = ' ')
+{
+	vector<string> words;
+	stringstream   strm{ line };
+
+	for ( string word; getline(strm, word, sep); ) {
+		words.emplace_back(word);
+	}
+
+	return words;
+}
+
+vector<Instruction>
+read_file(const filesystem::path& filename)
+{
+	ifstream input{ filename };
+
+	vector<Instruction> instructions;
+
+	for ( string line; getline(input, line); ) {
+		const auto words = split_words(line);
+
+		if ( words.at(0) == "cpy" ) {
+			instructions.emplace_back(OpCode::CPY, Argument(words.at(1)), Argument(words.at(2)));
+		}
+		else if ( words.at(0) == "inc" ) {
+			instructions.emplace_back(OpCode::INC, Argument(words.at(1)));
+		}
+		else if ( words.at(0) == "dec" ) {
+			instructions.emplace_back(OpCode::DEC, Argument(words.at(1)));
+		}
+		else if ( words.at(0) == "jnz" ) {
+			instructions.emplace_back(OpCode::JNZ, Argument(words.at(1)), Argument(words.at(2)));
+		}
+		else if ( words.at(0) == "out" ) {
+			instructions.emplace_back(OpCode::OUT, Argument(words.at(1)));
+		}
+		else {
+			cerr << "unknown opcode..." << '\n';
+		}
+	}
+
+	return instructions;
+}
+
+#define JIT
+
+string
+execute(memory_type& memory, vector<Instruction> instructions)
+{
+	string result;
+
+	for ( size_t ip = 0; ip < instructions.size(); ) {
+		const auto& instruction = instructions.at(ip);
+
+		// cout << "#" << ip << " - " << memory['a'] << ", " << memory['b'] << ", " << memory['c'] << ", " << memory['d'] << ": " << (int) instruction.opCode << '\n';
+
+		switch ( instruction.opCode ) {
+			using enum OpCode;
+		case CPY:
+			memory[instruction.y->reg()] = instruction.x->eval(memory);
+			++ip;
+			break;
+		case INC:
+			memory[instruction.x->reg()]++;
+			++ip;
+			break;
+		case DEC:
+			memory[instruction.x->reg()]--;
+			++ip;
+			break;
+		case JNZ:
+			if ( instruction.x->eval(memory) != 0 ) {
+				ip += static_cast<size_t>(instruction.y->eval(memory));
+			}
+			else {
+				++ip;
+			}
+			break;
+		case OUT:
+			result += to_string(instruction.x->eval(memory));
+			if ( result.size() >= 20 ) {
+				ip = instructions.size();
+			}
+			else {
+				++ip;
+			}
+		}
+	}
+
+	return result;
+}
+
+void
+part1(const vector<Instruction>& instructions)
+{
+	for ( int seed = 0;; ++seed ) {
+		map<char, int> memory;
+
+		memory['a'] = seed;
+		memory['b'] = 0;
+		memory['c'] = 0;
+		memory['d'] = 0;
+
+		auto result = execute(memory, instructions);
+
+		if ( result == "01010101010101010101" ) {
+			cout << "Part1: " << seed << '\n';
+			return;
+		}
+	}
+}
+
+} // namespace
+
+int
+main()
+{
+	const auto instructions = read_file("data/day25.txt");
+	try {
+		part1(instructions);
+	}
+	catch ( exception& e ) {
+		cerr << e.what() << '\n';
+	}
+}
-- 
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