Codeforces celebrates 10 years! We are pleased to announce the crowdfunding-campaign. Congratulate us by the link https://codeforces.com/10years. ×

Rei's blog

By Rei, 9 years ago, translation, ,
Problem C.
Vladimir wins exactly when there is a pie with distance to the border not greater than 4. Indeed if there is such a pie, then Vladimir will move it to the border and then move it around the whole rim. Of course if there would be any chance to throw this pie from the board, Vladimir will use it. If he gets no such chance, then after mentioned moves all border is banned. But it means Vlad made at least 2n + 2m turns, when Vladimir only 2n + 2m - 1 as a maximum. A contradiction. Else, if there is no such pie, then during first 4 turns Vlad would ban sides adjacent to each corner of the board. After that, if some pie comes to the rim he would ban adjacent side (there is no more than one such side) ans so Vladimir will never get the pie.

So solution consists of only one distance check, but, as one may see, it is easy to make mistake.

• +17

 9 years ago, # |   0 So, the most important thing to notice was, "when a pie reaches corner , it has two escape routes". So the 2nd player has to make one extra block at each corner...thats why the thing "4" comes in picture...  hmmmm....Good Problem.
 9 years ago, # |   +1 Grrr. Got this one straight up but got a couple of off-by-ones. A good problem. Costed me a few rating points. :(. Need to be more careful next time. Anyone else get the same kind of error?