Linked list with multiple parent and child nodes

Question

I am trying to design a program that takes in data from a file, after which it gives numbering to unique data, linked list also contains parent and child lists.

Data

Answer 1

You could try to separate the data from the data structure by implementing lists of pointers to data objects:

struct data_item {
    unsigned char data;
    unsigned char id;
    unsigned int  count;
    // Whatever other data you want.
};

struct list_node {
    struct data_item *item;
    struct list_node *next;
}

Now, as we encounter characters in the file, we insert them into a "repository" data structure. For this example I'll use a simple table, but you can use a list if you want to save space or a tree if you want to save space while maintaining fast search speeds, etc.

data_item data_table[UCHAR_MAX + 1] = {0};
...

unsigned char data = read_character_from_file();
struct data_item *di = data_table[data];

if (di == NULL)
    di = new_data_item(data);
else
    ++di->count;

And attach them to the current list:

struct list_node *list;
if (first_item_in_list())
    list = new_list(di)
else
    list - add_list(list, di);

Now you can have as many such lists as you want (even a list-of-lists if you don't know the number of lists in advance).