Advent of Code Day 3 Part 1

day3_part1.c

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

static char get_priority(char c)
{
    if (c >= 'a' && c <= 'z') {
        return c - 96;
    } else if (c >= 'A' && c <= 'Z') {
        return c - 38;
    } else {
        fprintf(stderr, "Invalid input\n");
        exit(-1);
    }
}

int main(void)
{
    int fd = open("input", O_RDONLY);
    if (fd == -1) {
        perror("open");
        return -1;
    }
    char line[128];
    char buffer[4096];
    bool priorities[53];
    ssize_t bytes;
    int line_index = 0;
    size_t answer = 0;
    while((bytes = read(fd, buffer, 4096)) > 0) {
        for (ssize_t i = 0; i < bytes; i++) {
            if (buffer[i] == '\n') {
                if (line_index % 2 != 0) {
                    fprintf(stderr, "Odd line length\n");
                    return -1;
                }
                memset(priorities, 0, 53 * sizeof(bool));
                int compartment2 = line_index / 2;
                for (int j = 0; j < compartment2; j++) {
                    priorities[line[j]] = true;
                }
                for (int j = compartment2; j < line_index; j++) {
                    if (priorities[line[j]]) {
                        answer += line[j];
                        break;
                    }
                }
                line_index = 0;
            } else {
                line[line_index++] = get_priority(buffer[i]);
            }
        }
    }
    printf("Answer: %ld\n", answer);
    return 0;
}