For this round I wrote the problems. I hope you find them interesting! wanbo tested them, and other contributors (pre-solving, suggestions, technical help, etc.) are malcolm, satyaki3794, and Shafaet. Thank you for all your help!
The top 10 will get awesome HackerRank t-shirts. Editorials will be available at the end. Good luck and have fun!
Update: Score distribution : 30-50-80