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2 player game, green and red tokens on 2021 x 2023 board

Source: 2022 Mathematics Regional Olympiad of Mexico West P6

October 6, 2022
combinatoricsgamegame strategywinning strategy

Problem Statement

There is a 2021×20232021 \times 2023 board that has a white piece in the central square, on which Mich and Moka are going to play in turns. First Mich places a green token on any free space so that it is not in the same row or column as the white token, then Moka places a red token on any free space so that it is not in the same row or column as the white token. white or green. From now on, Mich will place green tokens and Moka will place red tokens alternately according to the following rules: \bullet For the placed piece there must be another piece of the same color in its row or column, such that there is no other piece between both pieces. \bullet If there is at least one box that meets the previous rule, then it is mandatory to place a token. When a token is placed, it changes all the tokens that are on squares adjacent to it to the same color. The game ends when one of the players can no longer place tiles. If when the game ends the board has more green tiles then Mich wins, and if it has more red tiles then Moka wins. Determine if either player has a winning strategy.