day9part2.cpp

#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <exception>

struct Event
{
	enum
	{
		none = 0,
		output = 1,
		input = 2
	}type = none;
	long long* var = nullptr;
	operator bool()
	{
		return type != none;
	}
};

constexpr size_t pow(size_t a, size_t b)
{
	if(b == 0)
	{
		return 1;
	}
	size_t res = a;
	for(size_t i = 1; i < b; ++i)
	{
		res *= a;
	}
	return res;
}

class Intmachine
{
public:
	std::vector<long long> memory;
	Intmachine(const std::string_view Intcode)
	{
		std::ifstream ifs(Intcode.data());
		for(long i; ifs >> i; ifs.ignore())
		{
			memory.push_back(i);
		}
		memory.resize(memory.size() * 128, 0);
	}
	size_t relBase = 0;
	size_t instr_ptr = 0;
	long long &getVar(unsigned char param)
	{
		unsigned char mode = (memory[instr_ptr]/(10*pow(10, param))) % 10;
		switch(mode)
		{
			case 0:
				return memory[memory[instr_ptr + param]];
				break;
			case 1:
				return memory[instr_ptr + param];
				break;
			case 2:
				return memory[memory[instr_ptr + param] + relBase];
				break;
			default:
				std::terminate();
		}
	}
	Event step()
	{
		switch(memory[instr_ptr]%100)
		{
			case 1:
				getVar(3) = getVar(1) + getVar(2);
				instr_ptr += 4;
				break;
			case 2:
				getVar(3) = getVar(1) * getVar(2);
				instr_ptr += 4;
				break;
			case 3:
			{
				Event e{Event::input, &getVar(1)};
				instr_ptr += 2;
				return e;
			}
			case 4:
			{
				Event e{Event::output, &getVar(1)};
				instr_ptr += 2;
				return e;
			}
			case 5:
				if(getVar(1))
				{
					instr_ptr = getVar(2);
					break;
				}
				instr_ptr += 3;
				break;
			case 6:
				if(!getVar(1))
				{
					instr_ptr = getVar(2);
					break;
				}
				instr_ptr += 3;
				break;
			case 7:
				getVar(3) = getVar(1) < getVar(2);
				instr_ptr += 4;
				break;
			case 8:
				getVar(3) = getVar(1) == getVar(2);
				instr_ptr += 4;
				break;
			case 9:
				relBase += getVar(1);
				instr_ptr += 2;
				break;
			default:
				std::cerr << "Unknown opcode " << memory[instr_ptr] << '\n';
				std::terminate();
				break;
		}
		return Event();
	}
	Event run()
	{
		while(memory[instr_ptr] != 99)
		{
			Event e = step();
			if(e.type)
			{
				return e;
			}
		}
		return Event();
	}
};

int main()
{
	Intmachine machine("input.txt");
	while(Event e = machine.run())
	{
		if(e.type == Event::input)
		{
			*e.var = 2;
		}
		else
		{
			std::cout << *e.var << '\n';
		}
	}
	return 0;
}