day2.cpp

/*
 * =====================================================================================
 *
 *       Filename:  day2.cpp
 *
 *    Description: Day 2 of Advent of Code solution 
 *
 *        Version:  1.0
 *        Created:  12/2/2019 6:20:07 PM
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  invakid404
 *
 * =====================================================================================
 */


#include <bits/stdc++.h>

#define IN_PATH R"(D:\Coding\Problems\adventofcode\in\day2.txt)"
#define ENDL '\n';
#define RANGE(i, a, b, s) for(auto i = a; i < b; i += s)

namespace {
	auto split(const std::string& s, char d) -> std::vector<std::string> {
		std::vector<std::string> result;
		
		std::stringstream ss(s);
		std::string curr;

		while(std::getline(ss, curr, d)) {
			result.emplace_back(curr);
		}

		return result;
	}
	
	auto handle_add(std::vector<int>& data, int idx) -> void {
		auto a = data[idx + 1];
		auto b = data[idx + 2];
		auto dest = data[idx + 3];

		data[dest] = data[a] + data[b];
	}

	auto handle_mult(std::vector<int>& data, int idx) -> void {
		auto a = data[idx + 1];
		auto b = data[idx + 2];
		auto dest = data[idx + 3];

		data[dest] = data[a] * data[b];
	}

	auto part_one(const std::vector<int>& opcodes, int n, int v) -> int {
		std::vector<int> data = opcodes;
		data[1] = n;
		data[2] = v;
		
		RANGE(i, 0LL, data.size(), 4) {
			auto curr = data[i];
			
			auto flag = false;
			switch(curr) {
			case 1:
				handle_add(data, i);
				break;
			case 2:
				handle_mult(data, i);
				break;
			case 99:
				flag = true;
				break;
			default:
				std::cerr << "How did this happen?" << ENDL;
			}

			if(flag) {
				break;
			}
		}

		return data[0];
	}

	auto part_two(const std::vector<int>& opcodes, int search) -> int {
		auto initial = part_one(opcodes, 0, 0);
		auto increase = part_one(opcodes, 1, 0) - 99 - initial;

		auto range = search - initial;
		
		auto d = std::div(range, increase);
		return d.quot + d.rem;
	}
}

int main() {
	std::ifstream f_in;

	f_in.open(IN_PATH);
	if(!f_in) {
		std::cerr << "Failed to open file!" << ENDL;
		return 1;
	}

	std::string data;
	std::getline(f_in, data);

	auto parts = split(data, ',');

	std::vector<int> opcodes(parts.size());
	std::transform(parts.begin(), parts.end(), opcodes.begin(), 
			[](const auto& val) {
				return std::stoi(val);
			});
	
	std::cout << part_one(opcodes, 12, 2) << ENDL;
	std::cout << part_two(opcodes, 19690720) << ENDL;

	return 0;
}