adventofcode2023/day15/c/day15.c

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

#define LINE_MAX_LENGTH 32*1024
#define STRBUF_SIZE 64
#define NUM_BOXES 256
#define MAX_LENS_PER_BOX 32
#define NUM_0_CHARCODE 48

typedef struct lens {
    char label[STRBUF_SIZE];
    int label_len;
    int focal_length;
} lens_t;

typedef struct box {
    lens_t lenses[MAX_LENS_PER_BOX];
    int lenses_num;
} box_t;

int hash(char*, int);

int main() {
    char *p, *buf, c, *start;

    buf = (char *)malloc(LINE_MAX_LENGTH);
    memset(buf, 0, LINE_MAX_LENGTH);
    p = buf;
    char strbuf[STRBUF_SIZE];
    memset(strbuf, 0, STRBUF_SIZE * sizeof(char));

    box_t boxes[NUM_BOXES];
    memset(boxes, 0, NUM_BOXES * sizeof(box_t));

    int sum = 0;
    while ((c = getchar()) != EOF) {
        *p++ = c;
        if (c == '\n') {
            p = buf;
            start = p;
            while (*p != '\0') {
                while (*p != ',' && *p != '\n') p++;
                strncpy(strbuf, start, p - start);
                sum += hash(strbuf, p - start);
                // Find = or -
                while (*p != '-' && *p != '=') p--;
                int box_num = hash(strbuf, p - start);
                if (*p == '-') {
                    for (int i = 0; i < boxes[box_num].lenses_num; i++) {
                        if (boxes[box_num].lenses[i].label_len == p - start && !strncmp(boxes[box_num].lenses[i].label, strbuf, p - start)) {
                            for (int j = i; j < boxes[box_num].lenses_num - 1; j++) {
                                memcpy(&boxes[box_num].lenses[j], &boxes[box_num].lenses[j + 1], sizeof(lens_t));
                            }
                            boxes[box_num].lenses_num--;
                            break;
                        }
                    }
                    p++;
                } else if (*p == '=') {
                    int found = 0;
                    int focal_length = *(p+1) - NUM_0_CHARCODE;
                    for (int i = 0; i < boxes[box_num].lenses_num; i++) {
                        if (boxes[box_num].lenses[i].label_len == p - start && !strncmp(boxes[box_num].lenses[i].label, strbuf, p - start)) {
                            boxes[box_num].lenses[i].focal_length = focal_length;
                            found = 1;
                            break;
                        }
                    }

                    if (!found) {
                        boxes[box_num].lenses[boxes[box_num].lenses_num].label_len = p - start;
                        boxes[box_num].lenses[boxes[box_num].lenses_num].focal_length = focal_length;
                        strncpy(boxes[box_num].lenses[boxes[box_num].lenses_num].label, strbuf, p - start);
                        boxes[box_num].lenses_num++;
                    }
                    p++;
                    p++;
                }

                p++;
                start = p;
                memset(strbuf, 0, STRBUF_SIZE * sizeof(char));
            }
            memset(buf, 0, LINE_MAX_LENGTH);
            p = buf;
        }
    }

    int part2 = 0;
    for (int i = 0; i < NUM_BOXES; i++) {
        for (int j = 0; j < boxes[i].lenses_num; j++) {
            part2 += (i+1) * (j+1) * boxes[i].lenses[j].focal_length;
        }
    }

    printf("%i\n", sum);
    printf("%i\n", part2);
    free(buf);
}

int hash(char *str, int len) {
    int current_value = 0;

    for (int i = 0; i < len; i++) {
        current_value += str[i];
        current_value *= 17;
        current_value %= 256;
    }

    return current_value;
}