Very good!

Insane, how is works? I understand how algorithm works but I can't get into the main idea.

Clear and nice!

Great solution! Only thing I do not understand is if the result is generated in the last level of recursion in two for loops, then why the recursion was used at all?

I see that all we recieve from all levels of recursion calls and comparing points in arrays split in half, is only definition of "mi", that is reassigned many times in for loop of the last recursion call.

I deleteted everything except these two for loops and sent original array sorted by 'Y', and it passed tests.