advent6.c

// Solution to advent of code, day 6

#include <ctype.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

// Part 1
bool lights[1000][1000] = {false};

// Part 2
int dimmable_lights[1000][1000] = {0};

// Checks if the light at (x, y) is within the limits {x0, y0, xend, yend}
bool is_in_range(int x, int y, int* limits)
{
	return (x >= limits[0]) && (x <= limits[2]) && (y >= limits[1]) && (y <= limits[3]);
}

// "482,293" -> {482, 293}
int* str_to_int_pair(char* pair_desc)
{
	static int result[] = {0, 0};

	// This will store one of the two numbers
	char* temp_substring = calloc(4, sizeof(char));

	// Will store the non-numeric part while converting char* to int. Not needed
	char* str_part;
	int pos = 0;

	// Copy everything before the comma in pair_desc to temp_substring
	for(; pair_desc[pos] != ','; pos++)
	{
		temp_substring[pos] = pair_desc[pos];
	}

	// Convert to int and store in result array
	result[0] = (int) strtol(temp_substring, &str_part, 10);

	// Skip the comma
	pos++;

	// Save the position where the second number starts
	int start_of_second_int = pos;

	// Clear the substring that stores one number
	memset(temp_substring, '\0', sizeof(temp_substring)/sizeof(char));

	// Copy everything after the comma in pair_desc to temp_substring
	for(; pair_desc[pos] != '\0'; pos++)
	{
		temp_substring[pos - start_of_second_int] = pair_desc[pos];
	}

	// Convert the second one to int too
	result[1] = (int) strtol(temp_substring, &str_part, 10);

	return result;
}


// "1,2 through 3,4" -> {1, 2, 3, 4}
int* decode_range(char* desc)
{
	int* results = calloc(4, sizeof(int));

	int pos = 0;
	char* tmp_desc = calloc(8, sizeof(char)); // 2 * 3-digit number + ',' + '\0'

	for(; desc[pos] != ' '; pos++)
	{
		tmp_desc[pos] = desc[pos];
	}

	// Convert to int[] and copy to first half of results
	int* start = str_to_int_pair(tmp_desc);
	memcpy(results, start, 2 * sizeof(int));

	// Skip over " through " until we have numbers again
	while (!isdigit(desc[pos]))
	{
		pos++;
	}

	int start_of_second_pair = pos;
	for(; desc[pos] != '\0'; pos++)
	{
		tmp_desc[pos - start_of_second_pair] = desc[pos];
	}

	// Convert to int[] and copy to second half of results
	int* end = str_to_int_pair(tmp_desc);
	memcpy(&(results[2]), start, 2 * sizeof(int));

	return results;
}

// command: -1 -> toggle, 1 -> on, 0 -> off
// part 2: -1 -> +2, 1 -> +1, 0 -> -1
void manipulate(char* desc, int command)
{
	int* area = decode_range(desc);
	int x0 = area[0];
	int y0 = area[1];
	int x1 = area[2];
	int y1 = area[3];

	for(int y = y0; y <= y1; y++)
	{
		for(int x = x0; x <= x1; x++)
		{
			switch(command)
			{
				case -1:
					lights[x][y] = !lights[x][y];
					dimmable_lights[x][y] += 2;
					break;
				case 0:
					lights[x][y] = 0;
					if(dimmable_lights[x][y] > 0)
					{
						dimmable_lights[x][y] -= 1;
					}
					break;
				case 1:
					lights[x][y] = 1;
					dimmable_lights[x][y] += 1;
					break;
			}
		}
	}
}

void parse_cmd(char* command)
{
	switch (command[6])
	{
		case ' ':
			manipulate(command + 7, -1);
			break;
		case 'n':
			manipulate(command + 8, 1);
			break;
		case 'f':
			manipulate(command + 9, 0);
			break;
	}
}

int count_lights_on()
{
	static int lights_on = 0;

	for (int y = 0; y < 1000; y++)
	{
		for (int x = 0; x < 1000; x++)
		{
			if (lights[x][y])
			{
				lights_on++;
			}
		}
	}
	return lights_on;
}

int total_brightness()
{
	static int brightness = 0;

	for (int y = 0; y < 1000; y++)
	{
		for (int x = 0; x < 1000; x++)
		{
			brightness += dimmable_lights[x][y];
		}
	}

	return brightness;
}

int main(int argc, char** argv)
{

	FILE* inputFile = fopen("input6.txt", "r");
	char line[64];

	while(fgets(line, sizeof(line), inputFile))
	{
		// printf("%s", line);
		parse_cmd(line);
	}

	printf("Part 1: %d lights are on.\n", count_lights_on());

	printf("Part 2: Total brightness is %d.\n", total_brightness());

	return 0;
}