aoc2023/day5/p2.c

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


uint64_t parse_number(char *end);

#define MAPS_LEN 7

typedef struct {
    uint64_t dst, src, rng;
} map_t;


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

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

    if (getline(&line, &line_buf_length, input) == -1) {
        fprintf(stderr, "A file %s ended unexpectedly.", argv[1]);
        return -1;
    }

    char *colon_pos = strchr(line, ':');

    size_t seed_ranges_len = 0;
    for (char *space_pos = colon_pos+1; space_pos != NULL; space_pos = strchr(space_pos, ' ')) {
        seed_ranges_len++;
        space_pos++;
    }

    uint64_t *seed_ranges = (uint64_t *) calloc(seed_ranges_len, sizeof(uint64_t));
    for (size_t i = 0, seeds_pos = (size_t) colon_pos+2;; seeds_pos++) {
        while (*(char *)(seeds_pos)>>4 == 0x3) seeds_pos++;
        seed_ranges[i++] = parse_number((char *)(seeds_pos-1));
        if (*(char *)seeds_pos == '\n')
            break;
    }

    map_t **maps = (map_t **) calloc(MAPS_LEN, sizeof(map_t *));
    for (size_t i = 0; i < MAPS_LEN; ++i)
        maps[i] = (map_t *) calloc(1, sizeof(map_t));
    size_t map_lengths[MAPS_LEN] = {1};

    int8_t maps_cur = -1;
    while (getline(&line, &line_buf_length, input) != -1) {
        if (maps_cur == MAPS_LEN)
            break;
        if (line[0] == '\n') {
            maps_cur++;
            continue;
        } else if (line[0]>>4 != 0x3)
            continue;

        map_lengths[maps_cur]++;
        maps[maps_cur] = (map_t *) realloc(maps[maps_cur], map_lengths[maps_cur] * sizeof(map_t));

        map_t new_range_map = {0};
        sscanf(line, "%lu %lu %lu\n", &new_range_map.dst, &new_range_map.src, &new_range_map.rng);

        maps[maps_cur][map_lengths[maps_cur]-1] = new_range_map;

        memset(line, 0, line_buf_length);
    }

    uint64_t lowest_loc_n = UINT64_MAX;

    for (size_t i = 0; i < seed_ranges_len; i += 2)
        #pragma omp parallel for shared(lowest_loc_n)
        for (uint64_t r = seed_ranges[i]; r < seed_ranges[i] + seed_ranges[i+1]; ++r) {
            uint64_t seed = r;

            for (size_t j = 0; j < MAPS_LEN; ++j)
                for (size_t k = 0; k < map_lengths[j]; ++k)
                    if (seed >= maps[j][k].src && seed <= maps[j][k].src + maps[j][k].rng) {
                        seed = maps[j][k].dst + (seed - maps[j][k].src);
                        break;
                    }

            if (seed < lowest_loc_n)
                lowest_loc_n = seed;
        }

    free(seed_ranges);

    for (size_t i = 0; i < MAPS_LEN; ++i)
        free(maps[i]);

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

    return 0;
}

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

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

    return num;
}