From e352e71da81a66c75230a36fbf909f91ae54e963 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Fri, 17 Oct 2025 09:40:13 +0200
Subject: day 12, aoc 2016

---
 2016/src/day12.cpp | 188 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 188 insertions(+)
 create mode 100644 2016/src/day12.cpp

(limited to '2016/src/day12.cpp')

diff --git a/2016/src/day12.cpp b/2016/src/day12.cpp
new file mode 100644
index 0000000..1e231a5
--- /dev/null
+++ b/2016/src/day12.cpp
@@ -0,0 +1,188 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <optional>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+enum class OpCode : uint8_t {
+	CPY_VAL,
+	CPY_REG,
+	INC,
+	DEC,
+	JMP,
+	JNZ,
+};
+
+struct Instruction {
+	Instruction(OpCode opCode, char reg)
+	    : opCode{ opCode }
+	    , reg{ reg }
+	{
+	}
+
+	Instruction(OpCode opCode, int val)
+	    : opCode{ opCode }
+	    , val{ val }
+	{
+	}
+
+	Instruction(OpCode opCode, char reg, int val)
+	    : opCode{ opCode }
+	    , reg{ reg }
+	    , val{ val }
+	{
+	}
+
+	OpCode         opCode;
+	optional<char> reg;
+	optional<int>  val;
+};
+
+/*
+ostream&
+operator<<(ostream& os, const Instruction& instruction)
+{
+    cout << (int) instruction.opCode << ":";
+    if ( instruction.reg.has_value() ) {
+        cout << " reg: " << instruction.reg.value();
+    }
+    if ( instruction.val.has_value() ) {
+        cout << " val: " << instruction.val.value();
+    }
+    return os;
+}
+*/
+
+vector<Instruction>
+read_file(const filesystem::path& filename)
+{
+	ifstream input{ filename };
+
+	vector<Instruction> instructions;
+
+	for ( string line; getline(input, line); ) {
+		if ( line.starts_with("cpy") ) {
+			if ( isalpha(line.at(4)) != 0 ) {
+				auto from_reg = line.at(4);
+				auto to_reg   = line.at(6);
+				instructions.emplace_back(OpCode::CPY_REG, to_reg, from_reg);
+			}
+			else {
+				auto val = stoi(&line.at(strlen("cpy ")));
+				auto reg = line.back();
+				instructions.emplace_back(OpCode::CPY_VAL, reg, val);
+			}
+		}
+		else if ( line.starts_with("inc") ) {
+			auto reg = line.at(4);
+			instructions.emplace_back(OpCode::INC, reg);
+		}
+		else if ( line.starts_with("dec") ) {
+			auto reg = line.at(4);
+			instructions.emplace_back(OpCode::DEC, reg);
+		}
+		else if ( line.starts_with("jnz 1") ) { // always jump!, WTF??
+			auto off = stoi(&line.at(strlen("jnz 1 ")));
+			instructions.emplace_back(OpCode::JMP, off);
+		}
+		else if ( line.starts_with("jnz") ) {
+			auto reg = line.at(4);
+			auto off = stoi(&line.at(strlen("jnz a ")));
+			instructions.emplace_back(OpCode::JNZ, reg, off);
+		}
+		else {
+			cerr << "unknown opcode..." << '\n';
+		}
+
+		// cout << line << " -> " << instructions.back() << '\n';
+	}
+
+	return instructions;
+}
+
+void
+execute(map<char, int>& memory, const vector<Instruction>& instructions)
+{
+	for ( size_t ip = 0; ip < instructions.size(); ) {
+		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_VAL:
+			memory[instruction.reg.value()] = instruction.val.value();
+			++ip;
+			break;
+		case CPY_REG:
+			memory[instruction.reg.value()] = memory[static_cast<char>(instruction.val.value())];
+			++ip;
+			break;
+		case INC:
+			memory[instruction.reg.value()]++;
+			++ip;
+			break;
+		case DEC:
+			memory[instruction.reg.value()]--;
+			++ip;
+			break;
+		case JMP:
+			ip += static_cast<size_t>(instruction.val.value());
+			break;
+		case JNZ:
+			if ( memory[instruction.reg.value()] != 0 ) {
+				ip += static_cast<size_t>(instruction.val.value());
+			}
+			else {
+				++ip;
+			}
+			break;
+		}
+	}
+}
+
+void
+part1(const vector<Instruction>& instructions)
+{
+	map<char, int> memory;
+
+	memory['a'] = 0;
+	memory['b'] = 0;
+	memory['c'] = 0;
+	memory['d'] = 0;
+
+	execute(memory, instructions);
+
+	cout << "Part1: " << memory['a'] << '\n';
+}
+
+void
+part2(const vector<Instruction>& instructions)
+{
+	map<char, int> memory;
+
+	memory['a'] = 0;
+	memory['b'] = 0;
+	memory['c'] = 1;
+	memory['d'] = 0;
+
+	execute(memory, instructions);
+
+	cout << "Part2: " << memory['a'] << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+	const auto instructions = read_file("data/day12.txt");
+	part1(instructions);
+	part2(instructions);
+}
-- 
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