AoC2024/12/main.c

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

struct list {
	char type;
	struct square *tiles;
	unsigned int area;
	unsigned int perimeter;
	struct list *next;
};
struct square {
	int x;
	int y;
	struct square *next;
};

bool tile_in_list(int x, int y, struct list *plot)
{
	if (!plot)
		return 0;
	struct square *current = plot->tiles;
	while (current) {
		if (current->x == x && current->y == y) {
			return 1;
		}
		current = current->next;
	}
	return 0;
}

bool plot_exists (int x, int y, struct list *plots)
{
	struct list *current = plots;
	while (current) {
		if (tile_in_list(x, y, current))
			return 1;
		current = current->next;
	}
	return 0;
}

void add_tile(int x, int y, struct list *plot)
{
	if (plot->tiles == NULL) {
		plot->tiles = malloc(sizeof(struct square));
		plot->tiles->x = x;
		plot->tiles->y = y;
		plot->tiles->next = NULL;
		return;
	}

	struct square *tiles = plot->tiles;
	while (tiles->next)
		tiles = tiles->next;

	tiles->next = malloc(sizeof(struct square));
	tiles->next->x = x;
	tiles->next->y = y;
	tiles->next->next = NULL;
}

struct list *check_plot(int x, int y, int width, int height, char **map, struct list *plot, bool daddy)
{
	int dir[4][2] = {{0, -1}, {1, 0}, {0, 1}, {-1, 0}};
	int perimeter = 0;
	// daddy simply states if this function was called from the outside,
	// since the main loop will never send grids in the same plot
	// should actually be solved by handling the list outside this func

	struct list *prevPlot = plot;
	while (plot && plot->type != map[x][y]) {
		prevPlot = plot;
		plot = plot->next;
	}
	// create list of every tile in this plot
	// init list
	if (plot == NULL || daddy) {
		plot = malloc(sizeof(struct list));
		plot->type = map[x][y];
		plot->area = 0;
		plot->perimeter = 0;
		plot->tiles = NULL;
		plot->next = NULL;
		if (prevPlot)
			prevPlot->next = plot;
	}
	// check if current tile is in this list
	// if yes, return
	if (tile_in_list(x, y, plot))
			return NULL;
	// else, add, then check all surrounding tiles with this function
	add_tile(x, y, plot);
	plot->area++;

	// look in every direction for same type, recurse it
	for (int i = 0; i < 4; i++) {
		if (x + dir[i][0] >= 0 &&
		    x + dir[i][0] < width &&
		    y + dir[i][1] >= 0 &&
		    y + dir[i][1] < height) {
			if (map[x + dir[i][0]][y + dir[i][1]] == map[x][y]) {
				check_plot(x + dir[i][0], y + dir[i][1],
				            width, height, map, plot, false);
			} else {
				plot->perimeter++;
			}
		} else
			plot->perimeter++;
	}
	return plot;
}

int main ()
{
	// figure out data dimensions
	FILE *input = fopen("./input", "r");
	int width =  0;
	int height = 1;
	while (fgetc(input) != '\n') width++;
	for (char c = fgetc(input); c != EOF; c = fgetc(input)) {
		if (c == '\n')
			height++;
	}
	rewind(input);
	printf("Dimensions: %d x %d\n", width, height);

	// make 2d array
	char **map = malloc(width * sizeof(char*));
	map[0] = malloc(width * height);
	for (int i = 1; i < width; i++) {
		map[i] = map[0] + i * height;
	}

	// put the data in the array
	for (int i = 0; i < height; i++) {
		for (int j = 0; j < width; j++) {
			map[j][i] = fgetc(input);
		}
		fgetc(input);
	}
	fclose(input);

	int scoreSum = 0;
	// find plots not in list, check their score
	struct list *plots = NULL;
	struct list *current = NULL;
	char prevType = 0;
	for (int i = 0; i < height; i++) {
		for (int j = 0; j < width; j++) {
			// nasty if. prev type, skip. first, init head.
			// else, if tile is already in plot-list, skip
			// else, add a new plot to the list from current tile
			if (map[j][i] == prevType)
				continue;
			if (i == 0 && j == 0) {
				plots = check_plot(j,i, width, height, map, plots, true);
				current = plots;
			}
			else if (plot_exists(j, i, plots))
				continue;
			else
				current = check_plot(j,i, width, height, map, current, true);
		}
	}
	current = plots;
	int sum = 0;
	while (current) {
		printf("plot %c is area %d and perimeter %d\n", current->type, current->area, current->perimeter);
		sum += current->area * current->perimeter;
		current = current->next;
	}

	printf("total score: %d\n", sum);
}