Advent-of-Code/2024/2/main_pt2.cpp

#include <fstream>
#include <iostream>
#include <set>
#include <sstream>
#include <string>
#include <vector>

bool GroupSafe(const std::vector<long> &group);

int main()
{
	std::ifstream ifs("data.txt");
	if(!ifs.is_open())
	{
		std::cerr << "Missing data.txt." << std::endl;
		return -1;
	}

	unsigned long total = 0;
	unsigned long total_pt2 = 0;

	std::vector<std::vector<long>> data;

	for(std::string line; std::getline(ifs, line); )
	{
		if(line == "")
			continue;

		// add a row for this line:
		data.push_back({});

		std::istringstream input(line);
		// for each value in the line:
		for(std::string value; std::getline(input, value, ' '); )
		{
			try {
				// add it to the row
				data.back().push_back(std::atoi(value.c_str()));
			} catch (const std::exception &e) {
				break;
			}
		}
	}

	// DEBUG:
	// for(auto row : data)
	// {
	// 	for(auto col : row)
	// 		std::cout << col << " ";
	// 	std::cout << std::endl;
	// }

	for(auto group : data)
	{
		switch(group.size())
		{
		case 0:
			// Go to next line
			continue;
			break;
		case 1:
			// Can't be increasing or decreasing because it's the only one, so I guess safe?
			++total;
			++total_pt2;
			continue;
			break;
		};

		bool safe = true;

		if(GroupSafe(group))
			++total;
		else
		{
			bool re_safe = false;
			for(auto i = 0; i < group.size(); ++i)
			{
				std::vector<long> check;
				if(i != 0)
					check = { group.begin(), group.begin() + i };
				if(i < group.size() - 1)
					check.insert(check.end(), group.begin() + i + 1, group.end());
				if(GroupSafe(check))
				{
					re_safe = true;
					++total_pt2;
					break;
				}
			}
			if(!re_safe)
			{
				std::cout << "Bad: ";
				for(auto val : group)
					std::cout << val << " ";
				std::cout << std::endl;
			}
		}
	}
	std::cout << "    Total: " << total << std::endl;
	std::cout << "PT2 Total: " << total + total_pt2 << std::endl;

	return 0;
}


bool GroupSafe(const std::vector<long> &group)
{
	bool increasing = false;
	for(auto i = 0; i < group.size() - 1; ++i)
	{
		if(group[i] == group[i+1])
			continue;
		increasing = group[i] < group[i+1];
		break;
	}

	bool safe = true;
	int *last = nullptr;
	for(auto i = 0; i < group.size(); ++i)
	{
		auto next = group[i];

		if(!last)
		{
			last = new int(next);
			continue;
		}

		if(increasing &&
		   (next - *last < 1 || next - *last > 3))
			safe = false;
		else if(!increasing &&
		        (next - *last < -3 || next - *last > -1))
			safe = false;

		if(!safe)
			break;

		*last = next;
	}

	if(last)
		delete last, last = nullptr;

	return safe;
}