Hey if it would be really thankful if you could share somelinks of questions from previous contests and practice section pertaining to hashing and graphs.
Thanks.
The following link has a wonderful collection of tutorials and problems relating to wide variety of topics in algorithms:
At serial number 27, you will find graphs (materials and problems).
As far as hashing is related, go through the Rabin-Karp algorithm, listed at sixth position.
Also, the following link has some nice examples (solved problems) and explanations related to hashing:
http://threads-iiith.quora.com/String-Hashing-for-competitive-programming
You may find below link useful: