I got MLE in this submission. After investigation it turned out that I created empty containers before a recursive call (in the get_delete_x_ans function), resulting in creation of many such containers when call stack is deep.

That sounds reasonable, but when I did the calculation, it seemed impossible that this mistake could lead to MLE when the mem limit is 512MB.

So the calculation goes:

My later accepted solution uses 175100KB, limit is ~524288KB, difference is 300000+KB = approx. 300MB.

So it means that the submission above created empty containers that take up 300MB space.

It will create 2 empty queue, each is 48 byte on a 64-bit machine.

Recursion depth is <=500000 from problem description. So total space of empty containers is 2 x 48B x 500000 = approx. 5x10^7 B = 50MB.

That's much less than 300MB, so if the calculation was correct, I shouldn't get MLE.

Can someone help point out what's wrong with my calculation above? Thanks!