MathDB
2-player game on a m x n board

Source: 2021 Dutch IMO TST 2.2

December 28, 2021
combinatoricsgame strategygamewinning strategy

Problem Statement

Stekel and Prick play a game on an m×n m \times n board, where mm and nn are positive are integers. They alternate turns, with Stekel starting. Spine bets on his turn, he always takes a pawn on a square where there is no pawn yet. Prick does his turn the same, but his pawn must always come into a square adjacent to the square that Spike just placed a pawn in on his previous turn. Prick wins like the whole board is full of pawns. Spike wins if Prik can no longer move a pawn on his turn, while there is still at least one empty square on the board. Determine for all pairs (m,n)(m, n) who has a winning strategy.