using STL - http://www.techiedelight.com/data-structures-and-algorithms-...

check implementation of Trie - http://www.techiedelight.com/trie-implementation-insert-sear...

http://www.techiedelight.com/memory-efficient-trie-implement...

you can refer http://www.techiedelight.com/list-of-problems/

some of them are in C++ but you can easily follow if you know C

PDF of all problems - http://www.techiedelight.com/wp-content/uploads/Techie-Delig...