AdventOfCode C 2024 day 7

#include <stdio.h>
#include <stdbool.h>
#define SIZE 850
#define COL 20

int parse(FILE* file, long int* results, int items[][COL], int* sizes) {
    int index = 0;
    while (fscanf(file, "%ld: ", (results + index)) == 1) {
        int val;
        int offset = 0;
        char c;
        while (fscanf(file, "%d", &val) == 1) {
            items[index][offset++] = val;
            if ((c = fgetc(file)) != ' ') {
                // End of this string of values
                sizes[index] = offset;
                index++;
                offset = 0;
                break;
            }
        }
    }
    return index;
}

bool evaluate(long int result, long int current, int* items, int size_remaining, bool part_one) {
    if (size_remaining == 0) {
        return result == current;
    }
    if (evaluate(result, current + *items, items + 1, size_remaining - 1)) {
        return true;
    }
    if (evaluate(result, current * *items, items + 1, size_remaining - 1)) {
        return true;
    }
    if (part_one) {
        // Don't try ||
        return false;
    }
    int val = *items;
    // Get number of digits of val. shift current by that.
    do {
        val = val / 10;
        current *= 10;
    } while (val != 0);
    current += *items;
    bool concat = evaluate(result, current, items + 1, size_remaining - 1);
    return concat;
}

long int part_one(long int* results, int items[][COL], int* sizes, int size) {
    long int total = 0;
    for (size_t i = 0; i < size; i++) {
        long int res = *(results + i);
        int* values = items[i];
        int size = *(sizes + i);
        if (evaluate(res, *values, values + 1, size - 1, true)) {
            total += res;
        }
    }
    return total;
}
long int part_two(long int* results, int items[][COL], int* sizes, int size) {
    long int total = 0;
    for (size_t i = 0; i < size; i++) {
        long int res = *(results + i);
        int* values = items[i];
        int size = *(sizes + i);
        bool success = evaluate(res, *values, values + 1, size - 1, false);
        if (success) {
            total += res;
        }
    }
    return total;
}

int main() {
    FILE* file = fopen("2024-7.txt", "r");
    long int results[SIZE];
    int sizes[SIZE];
    int items[SIZE][COL];
    int size = parse(file, results, items, sizes);
    printf("Part one: %ld\n", part_one(results, items, sizes, size));
    printf("Part two: %ld\n", part_two(results, items, sizes, size));
}