IMO Shortlist 2010 problem C3

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Dodao/la: arhiva
23. lipnja 2013.
2500 chess kings have to be placed on a 100 \times 100 chessboard so that

(i) no king can capture any other one (i.e. no two kings are placed in two squares sharing a common vertex);
(ii) each row and each column contains exactly 25 kings.

Find the number of such arrangements. (Two arrangements differing by rotation or symmetry are supposed to be different.)

Proposed by Sergei Berlov, Russia
Izvor: Međunarodna matematička olimpijada, shortlist 2010