Reddit Daily Programmer #350 easy

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#define MAXSTR 1000

long longCompare(const void *a, const void *b) {
    return -1 * (*(long *) a - *(long *) b);
}

int read_input(char *filename, long **shelves, long **books, int *nShelves, int *nBooks, int *maxBooksWidth) {
    FILE *in = fopen(filename, "r");
    long tmp;
    char *shelves_width_s = malloc(MAXSTR * sizeof(char));
    int n = 0, N = 3;
    *shelves = malloc(N * sizeof(long));

    int k = 0, K = 3;
    *books = malloc(N * sizeof(long));

    // Read the shelves widths
    fgets(shelves_width_s, MAXSTR, in);
    char *tmpC = shelves_width_s;
    while ((tmp = strtol(tmpC, &tmpC, 10)) != 0) {
        if (n >= N) {
            N *= 2;
            *shelves = realloc(*shelves, N * sizeof(long));
        }
        *(*shelves + n++) = tmp;
    }
    *nShelves = n;

    //Read the books widths
    while (fscanf(in, "%ld %*s", &tmp) == 1) {
        if (k >= K) {
            K *= 2;
            *books = realloc(*books, K * sizeof(long));
        }
        *(*books + k++) = tmp;
        (*maxBooksWidth) += tmp;
    }
    *nBooks = k;
    free(shelves_width_s);
}

int solve(long *shelves, const long *books, int nShelves, int nBooks, int maxBooksWidth) {
    int currShelf = 0;
    int *markBooks = malloc(nBooks * sizeof(int));
    int *markShelves = malloc(nShelves * sizeof(int));
    long *shelvesCopy = malloc(nShelves * sizeof(long));
    memcpy(shelvesCopy, shelves, nShelves * sizeof(long));

    for (int k = 0; k < nBooks; k++)
        markBooks[k] = 0;
    for (int k = 0; k < nShelves; k++)
        markShelves[k] = 0;

    for (int i = 0; i < nShelves && maxBooksWidth != 0; i++) {
        for (int j = 0; j < nBooks && maxBooksWidth != 0; j++) {
            if (!markBooks[j] && shelvesCopy[i] >= books[j]) {
                currShelf = i;
                markShelves[i] = 1;
                shelvesCopy[i] -= books[j];
                maxBooksWidth -= books[j];
                markBooks[j] = 1;
            }
        }
    }
    if (maxBooksWidth == 0) {
        printf("Shelves to buy: %d\n", currShelf + 1);
        for (int i = 0; i <= currShelf; i++)
            printf("%ld ", shelves[i]);
    } else
        printf("Impossible\n");
}

int main() {
    long *shelves;    //Contains the shelves width
    int nShelves;
    long *books;    //Contains the books width
    int nBooks;
    int maxBooksWidth = 0;

    read_input("input.txt", &shelves, &books, &nShelves, &nBooks, &maxBooksWidth);
    qsort(shelves, nShelves, sizeof(long), longCompare);
    qsort(books, nBooks, sizeof(long), longCompare);
    solve(shelves, books, nShelves, nBooks, maxBooksWidth);
    return 0;
}