thanks for this fascinating input!

Everyone seems to complaining about the validation. What is really cool is the selection of rows and columns and square elements in just a few lines. This can be easily modified to use nested array instead of int.

wow. Beautifully written.

This is much better with linear time complexity. Also, easier to read.

Whew! This is actually really good. Love it. Group by and projection. Never thought of it.

It's only unreadable if you are unfamiliar with regular expressions. Otherwise, it's pretty straightforward.

Dear lord. This is not as readable. Good luck decipher this function without a name.