aoc2023/day4/p1.c

#define  _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>


uint64_t parse_number(char *end);


int main(int argc, char **argv) {
    FILE *input;
    char *line = NULL;
    size_t line_length = 0;

    if (argc == 1 || argv[1][0] == '-')
		input = stdin;
	else if ((input = fopen(argv[1], "r")) == NULL) {
		printf("Cannot open file %s\n", argv[1]);
		return -1;
	}

    uint64_t total_points = 0;

    size_t winning_numbers_len = 0;
    uint8_t *winning_numbers = NULL;
    char *colon_pos = NULL, *pipe_pos = NULL;

    while (getline(&line, &line_length, input) != -1) {
        colon_pos = strchr(line, ':');
        pipe_pos = strchr(line, '|');

        if (winning_numbers == NULL) {
            winning_numbers_len = (pipe_pos - colon_pos - 2) / 3;
            winning_numbers = (uint8_t *) calloc(winning_numbers_len, sizeof(uint8_t));
        }

        for (size_t i = 0, wl_pos = (size_t)colon_pos+4; i < winning_numbers_len; ++i, wl_pos += 3)
            winning_numbers[i] = parse_number((char *)(wl_pos-1));

        uint64_t points = 0;

        for (char *n_pos = pipe_pos + 4;; n_pos += 3) {
            uint8_t n = parse_number(n_pos-1);

            for (size_t i = 0; i < winning_numbers_len; ++i) {
                if (n != winning_numbers[i])
                    continue;
                points = (points == 0) ? 1 : points * 2;
                break;
            }

            if (*n_pos == '\n')
                break;
        }

        total_points += points;

        memset(line, 0, line_length);
    }

    free(winning_numbers);

    printf("%lu\n", total_points);

    return 0;
}

uint64_t parse_number(char *end) {
    uint64_t num = 0;

    for (size_t n = 1;; n *= 10) {
        if (*end>>4 != 0x3)
            break;
        num += (*end&0xf) * n;
        --end;
    }

    return num;
}