Simplest solution: Prepare required storages then Perform insert (with realloc if necessary)

Code Solution ------------------------>

int main() ........ { int total_number_of_shelves; scanf("%d", &total_number_of_shelves);

int total_number_of_queries;
scanf("%d", &total_number_of_queries);

//1. Prepare Storage
total_number_of_books = (int *)malloc(total_number_of_shelves * sizeof(int));
total_number_of_pages = (int **)malloc(total_number_of_shelves * sizeof(int*));

    //2. Init Storage
for (int i = 0; i < total_number_of_shelves; i++) 
{
    total_number_of_books[i] = 0;
    total_number_of_pages[i] = (int*)malloc(sizeof(int));
    total_number_of_pages[i][0] = 0;
}

while (total_number_of_queries--) {
    int type_of_query;
    scanf("%d", &type_of_query);

    if (type_of_query == 1) {
        /*
         * Process the query of first type here.
         */
        int x, y;
        scanf("%d %d", &x, &y);

                    //3. Insert Book
        total_number_of_books[x]++;

                    //4. Insert Page
        if(total_number_of_books[x] == 1)
        {
            total_number_of_pages[x][0] = y;
        }
        else 
        {
            total_number_of_pages[x] = realloc(total_number_of_pages[x], total_number_of_books[x]*sizeof(int));
            total_number_of_pages[x][total_number_of_books[x]-1] = y;
        }