Great find indeed. There were plenty of well thought-out challenges and I just wish I had more time to dedicate to them.
One curious question, though… (Google has failed me)
For many of the challenges, there was a note to output the results modulo 1000000007. (to prevent overflow, apparently) What I don’t understand is:
What does that even accomplish? I would reason that is no better an answer than % 1000000007.
What’s significant about the number choice 1000000007?