2023-day3.c

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

#define S 140

struct node
{
	int x, y;
	int n[2];
	struct node *next;
};

struct row
{
	char c[S+3];
};

struct map
{
	struct row r[S+2];
};

static struct map m;
static struct node *list;

static void push(int num, int x, int y)
{
	struct node **t, *n;

	for(t = &list; *t; t = &(*t)->next)
	{
		if((*t)->x != x || (*t)->y != y)
			continue;

		if((*t)->n[0] == 0)
		{
			(*t)->n[0] = num;
			return;
		}
		else if((*t)->n[1] == 0)
		{
			(*t)->n[1] = num;
			return;
		}
	}

	n = malloc(sizeof *n);
	n->x = x;
	n->y = y;
	n->n[0] = num;
	n->n[1] = 0;
	n->next = list;

	list = n;
}

static int ispuncty(int c)
{
	const char t[] = "*+$@/#&%=-";
	size_t i;

	for(i = 0; i < sizeof t; i++)
		if(c == t[i])
			return 1;

	return 0;
}

static int ispuncty2(int c)
{
	return c == '*';
}

#define D m.r[y+1].c[x+1]

const int xo[] = {-1,  0,  1, -1, 1, -1, 0, 1};
const int yo[] = {-1, -1, -1,  0, 0,  1, 1, 1};

static unsigned long part1_check_row(int y)
{
	int x = 0, num = 0, flag = 0;
	unsigned long total = 0;

	while(x <= S)
	{
		if(!isdigit(D) && num)
		{
			if(flag)
				total += num;
			flag = 0;
			num = 0;
		}

		else if(D == '.')
			;

		else if(isdigit(D))
		{
			int i;

			num *= 10;
			num += D - '0';

			for(i = 0; i < 8; i++)
				if(ispuncty(m.r[y+1+yo[i]].c[x+1+xo[i]]))
					flag = 1;
		}

		x++;
	}

	return total;
}

static unsigned long part1(void)
{
	int y;
	unsigned long total = 0;

	for(y = 0; y < S; y++)
	{
		total += part1_check_row(y);
	}

	return total;
}

static unsigned long part2_sum(void)
{
	struct node *n;
	unsigned long sum = 0;

	for(n = list; n; n = n->next)
		if(n->n[0] && n->n[1])
			sum += (n->n[0] * n->n[1]);

	return sum;
}

static void part2_check_row(int y)
{
	int x = 0, fx = 0, fy = 0, flag = 0, num = 0;

	while(x <= S)
	{
		if(!isdigit(D) && num)
		{
			if(flag)
				push(num, fx, fy);

			flag = 0;
			num = 0;
		}

		else if(D == '.')
			;

		else if(isdigit(D))
		{
			int i;

			num *= 10;
			num += D - '0';

			for(i = 0; i < 8; i++)
			{
				if(ispuncty2(m.r[y+1+yo[i]].c[x+1+xo[i]]))
				{
					flag = 1; fx = x+1+xo[i]; fy = y+1+yo[i];
				}
			}
		}

		x++;
	}
}

static unsigned long part2(void)
{
	int y;

	for(y = 0; y < S; y++)
		part2_check_row(y);

	return part2_sum();
}

int main(void)
{
	FILE *f;
	unsigned long total = 0;

	f = fopen(__FILE__ ".txt", "rb");
	if(!f)
	{
		fprintf(stderr, "idiot\n");
		return 0;
	}

	memset(&m, '.', sizeof (struct map));

	while(1)
	{
		char buf[256];
		static int i;

		if(!fgets(buf, 256, f))
			break;
		if(buf[0] == '\n' || buf[0] == '\r')
			break;
		*strchr(buf, '\r') = 0;

		memcpy(&m.r[i+1].c[1], buf, S);
		i++;
	}

	total = part1();
	printf("Part 1: %lu\n", total);

	total = part2();
	printf("Part 2: %lu\n", total);

	return 0;
}