Huge collection of data structure problems Mostly in C++ -

http://www.techiedelight.com/list-of-problems/

For other data structures, refer http://www.techiedelight.com/list-of-problems/

Below link has good set of tree problems in C++: http://www.techiedelight.com/list-of-problems/

Below link has good set of problems. Hope this helps: http://www.techiedelight.com/list-of-problems/

DSA problem set: http://www.techiedelight.com/list-of-problems/

> I know no path finding algorithms, and beyond arrays and hashes I don't know data structures like trees, double linked lists, and so on.

you can learn it from http://www.techiedelight.com/

Data Structure problems in C++ http://www.techiedelight.com/