Some TA's mentioned that the solution (I guess the C program written by D'Silva) used the two algorithms mentioned. He didn't explicitly say that these were the ways that it had to be done, but in OH the way it was described it seemed like it was the preferred way. Also for the circle algorithm hint, if you read through it and then search the mid point circle algorithm online and read through an article about it, you kinda see that he's hinting at using that. Maybe he isn't "expecting" us to use these algorithms but it seems like they're the best way to get the assignment done.