2022-day3.c

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

struct input
{
	size_t len;
	char line[1024];
};

static int score(char c)
{
	if(c >= 'a' && c <= 'z')
		return 1 + c - 'a';
	else if(c >= 'A' && c <= 'Z')
		return 27 + c - 'A';
	else
		abort();
}

static int p2(struct input *in)
{
	char baga[128] = {0}, bagb[128] = {0}, bagc[128] = {0};
	struct input *a, *b, *c;
	size_t i;

	a = &in[0];
	b = &in[1];
	c = &in[2];

	for(i = 0; i < 128; i++)
	{
		if(i < a->len)
			baga[a->line[i]] = 1;
		if(i < b->len)
			bagb[b->line[i]] = 1;
		if(i < c->len)
			bagc[c->line[i]] = 1;
	}

	for(i = 0; i < 128; i++)
	{
		if(baga[i] && bagb[i] && bagc[i])
		{
			return score(i);
		}
	}

	abort();
}

static int p1(struct input *in)
{
	char left[128] = {0}, right[128] = {0};
	size_t i, h;

	h = in->len/2;

	printf("Line: len %d, '%s'\n", in->len, in->line);

	for(i = 0; i < h; i++)
	{
		left[in->line[i]] = 1;
		right[in->line[i+h]] = 1;
	}

	for(i = 0; i < 128; i++)
	{
		if(left[i] && right[i])
			return score(i);
	}

	abort();
}

static int lineget(struct input *in, size_t max, FILE *f)
{
	char *p = in->line;
	size_t i;

	for(i = 0; i < max; i++)
	{
		int c = fgetc(f);

		if(c == EOF)
			return 0;

		*p = c;

		if(*p == '\n' || !*p)
		{
			*p = 0;
			break;
		}
		p++;
	}

	if(i == 0 || i == max)
		return 0;

	in->len = i;

	return 1;
}

int main(void)
{
	FILE *f;
	unsigned long p1sum = 0, p2sum = 0;
	f = fopen("day3.txt", "r");

	while(1)
	{
		struct input in[3];

		if(!lineget(&in[0], 1024, f))
			break;
		p1sum += p1(&in[0]);

		if(!lineget(&in[1], 1024, f))
			break;
		p1sum += p1(&in[1]);

		if(!lineget(&in[2], 1024, f))
			break;
		p1sum += p1(&in[2]);

		p2sum += p2(in);
	}

	printf("sum1: %lu, sum2: %lu\n", p1sum, p2sum);

	return 0;
}