Advent-of-Code/2024/6/main.cpp

#include <algorithm>
#include <fstream>
#include <iostream>
#include <map>
#include <set>
#include <sstream>
#include <string>
#include <unistd.h>
#include <vector>

enum Direction {
	UP = 0,
	RIGHT,
	DOWN,
	LEFT
};

struct Position {
	// NOTE(dev): Could do enum empty/reached/blocked, but I'm not interested.
	bool blocked = false;
	std::map<Direction, bool> reached;

	bool Reached() const {
		return reached.size();
	}
	char ReachedChar() const {
		bool up_or_down = false;
		bool left_or_right = false;
		if(reached.contains(Direction::UP) || reached.contains(Direction::DOWN))
			up_or_down = true;
		if(reached.contains(Direction::LEFT) || reached.contains(Direction::RIGHT))
			left_or_right = true;

		if(up_or_down != left_or_right)
		{
			if(up_or_down)
				return '|';
			else
				return '-';
		}
		else if(up_or_down)
			return '+';
		else
			return ' ';
	};
};

struct Player {
	std::pair<int, int> location;
	Direction direction = Direction::UP;
};

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

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

	std::map<std::pair<int, int>, Position> level;
	Player player;

	int max_x = 0;
	int max_y = 0;
	bool first_row = true;
	int y = 0;

	auto DebugPrint = [&]()
	{
		std::cout << std::endl;
		for(auto y = 0; y < max_y; ++y)
		{
			for(auto x = 0; x < max_x; ++x)
			{
				if(player.location.first == x && player.location.second == y)
				{
					switch(player.direction)
					{
					case Direction::UP:
						std::cout << "^";
						break;
					case Direction::RIGHT:
						std::cout << ">";
						break;
					case Direction::DOWN:
						std::cout << "v";
						break;
					case Direction::LEFT:
						std::cout << "<";
						break;
					};
				}
				else
				{
					const auto &pos = level[{x, y}];
					if(pos.Reached())
						std::cout << pos.ReachedChar();
					else if(pos.blocked)
						std::cout << "#";
					else
						std::cout << ".";
				}
			}
			std::cout << std::endl;
		}

		std::cout << std::endl;
		std::cout << "PT2 Total: " << total_pt2 << std::endl;
	};

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

		int x = 0;
		for(const char &value : line)
		{
			Position pos;
			if(value == '#')
				pos.blocked = true;
			if(value == '^') // always up?
			{
				pos.reached[Direction::UP] = true;
				player.location = {x, y};
			}

			level[{x, y}] = pos;

			++x;
		}
		if(first_row)
		{
			max_x = x;
			first_row = false;
		}
		++y;
	}
	max_y = y;

	// DEBUG:
	DebugPrint();

	std::cout << std::endl;

	while(true)
	{
		std::pair<int, int> next_location = player.location;
		switch(player.direction)
		{
		case Direction::UP:
			--next_location.second;
			break;
		case Direction::RIGHT:
			++next_location.first;
			break;
		case Direction::DOWN:
			++next_location.second;
			break;
		case Direction::LEFT:
			--next_location.first;
			break;
		};

		if(!level.contains(next_location))
		{
			player.location = next_location;
			break;
		}
		if(level[next_location].blocked)
		{
			// NOTE(dev): Also check if the next potential position is the last space before a turn,
			//             as then the up/down or left/right flag wouldn't be set, but the
			//             left/right or up/down flag would be.
			level[player.location].reached[player.direction] = true;
			player.direction = static_cast<Direction>(((int(player.direction)) + 1) % 4);
			level[player.location].reached[player.direction] = true;
		}
		else
		{
			// TODO(dev): Need to handle the scenario where you've yet to explore a section but it
			//             would result in a loop.
			//      e.g.: Placing a stopping point at the O
			//
			//    #     #
			//    +->O  #
			//   #|     #
			//    S #   #
			// #        #
			//     #    #
			//
			//      IDEA: Follow turns when exploring a direction like that.  Snake your way until
			//             you fall off the map or you line up with a square you've been in before
			std::map<Direction, bool> could_loop;
			// Part 2: If you could loop in this next position, COUNT IT
			if(player.direction == Direction::DOWN)
			{
				// search left of new position to see if you've been in this horizontal bit:
				for(int x = next_location.first; x >= 0; --x)
				{
					std::pair<int,int> potential_position = { x, next_location.second };
					if(level[potential_position].reached.contains(Direction::LEFT))
					{
						could_loop[Direction::LEFT] = true;
						break;
					}
				}
			}
			else if(player.direction == Direction::UP)
			{
				// search right of new position to see if you've been in this horizontal bit:
				for(int x = next_location.first; x < max_x; ++x)
				{
					std::pair<int,int> potential_position = { x, next_location.second };
					if(level[potential_position].reached.contains(Direction::RIGHT))
					{
						could_loop[Direction::RIGHT] = true;
						break;
					}
				}
			}
			else if(player.direction == Direction::LEFT)
			{
				// search left of new position to see if you've been in this horizontal bit:
				for(int y = next_location.second; y >= 0; --y)
				{
					std::pair<int,int> potential_position = { next_location.first, y };
					if(level[potential_position].reached.contains(Direction::UP))
					{
						could_loop[Direction::UP] = true;
						break;
					}
				}
			}
			else
			{
				// search left of new position to see if you've been in this horizontal bit:
				for(int y = next_location.second; y < max_y; ++y)
				{
					std::pair<int,int> potential_position = { next_location.first, y };
					if(level[potential_position].reached.contains(Direction::DOWN))
					{
						could_loop[Direction::DOWN] = true;
						break;
					}
				}
			}
			total_pt2 += could_loop.size();

			level[next_location].reached[player.direction] = true;
			player.location = next_location;

			DebugPrint();
			usleep(500000);
		}
	}

	DebugPrint();

	for(auto y = 0; y < max_y; ++y)
		for(auto x = 0; x < max_x; ++x)
			if(level[{x,y}].Reached())
				++total;

	std::cout << std::endl;
	std::cout << "    Total: " <<     total << std::endl;
	std::cout << "PT2 Total: " << total_pt2 << std::endl;

	return 0;
}