Saturday, March 16, 2013

SRM 573 editorial WIP: Div1 850: WolfPack

This was a great problem. Unfortunately it is also the kind of problem that has a trick that you either see or you don't. I would love to know what in the minds of target / red coders allows them to think of such creative ideas. But I don't.

My current plan is to finish the rest of the editorial tonight. Unfortunately my deteriorating health (I am not kidding) might get in the way and require me to add a whole day delay. But I will still try.

steve said...

Nice illustrations. What tools do you use to draw the figures in your editorials?

vexorian said...

Thanks. Inkscape.

RA said...

I wonder how can one come up with this transformation in such short time. Hey vexorian.. do you know of any previous problems that use this idea or did you get any information from writer/testers if this is just intuitive to them ? Thanks.

RA said...

and also, do you contact the writer/tester/some coders to discuss about the problem and solution ?

vexorian said...

I usually solve all problems but div1 hard alone.

The admins send me a short explanation and writer/tester solution for div1 hard some hours after every match ends. This is what I got for this problem:

"This time I believe the d1 hard was easy: rotate the entire board 45
degrees. Then you can solve the problem for each axes independently."

RA said...

I wish some of the high scored members can contribute to editorial too. Thanks for the reply.

I still don't get how transforming perpendicular movements to diagonal movements can help to achieve independency. I see in editorial some formal explanation, but I'm definitely missing some simple or (to-be) intuitive logic here :(

vexorian said...

That's the thing, high rated coders who were talking after the match would only say that they rotated the board, not why they thought of it.

There is no simple logic, only the formal idea, it is independent. Simplest logic be, that after rotating, each move changes both coordinates, instead of only one coordinate.