I'm one of the participants in this contest. The Zcash proof of work is Equihash. It uses Blake2b to create a bunch of hashes, then Wagner's generalized birthda

I'm one of the participants in this contest. The Zcash proof of work is Equihash. It uses Blake2b to create a bunch of hashes, then Wagner's generalized birthday algorithm to find a set of distinct hashes that xor to zero. The deadline is a little short at this point, but if you're decent at GPU programming it is achievable. Most of the other contestants are on the Zcash Slack.