Question

I’m using a naive approach to this problem, I’m putting the words in a linked list and just making a linear search into it. But it’s taking too much time in large files.

I was thinking in use a Binary Search Tree but I don’t know if it works good with strings. Also heard of Skip Lists, didn’t really learn it yet.

And also I have to use the C language…

Answer 1

The first upgrade to your algorithm could be having the list sorted, so, your lineal search could be faster (you only search until you find one element greater than yours), but this is still a naive solution.

Best approaches are Binary Search Trees and even better, a prefix tree (or trie, already mentioned in other answer).

In “The C Programming Language” From K&R you have the exact example of what you are looking for.
The first example of “autoreferenced data structs” (6.5) is a binary search tree used for counting the ocurrences of every word in a string. (You don’t need to count :P)

the structure is something like this:

struct tnode {
        char *word;
        struct tnode *left;
        struct tnode *right;
};

In the book you can see the whole example of what you want to do.

Binary Search Trees works good with any tipe of data structure that can accept an order, and will be better than a lineal search in a list.

Sorry for my poor english, and correct me if i was wrong with something I’ve said, Im very noob with C :p

EDIT: I can’t add comments to other answers, but I have read a coment from OP saying “The list isn’t sorted so I can’t use binary search”. It is nonsense to use binary search on a linked list. ¿Why? Binary Search is efficient when the access to a random element is fast, like in an array. In a double linked list, your worst access will be n/2.. However, you can put a lot of pointers in the list (accesing to key elements), but it is a bad solution..