MathDB
2 player game, k coins on intersections of n lines

Source: Rioplatense 2022 L3 p5

December 20, 2022
combinatoricsgame strategywinning strategygame

Problem Statement

Let n4n \ge 4 and kk be positive integers. We consider nn lines in the plane between which there are not two parallel nor three concurrent. In each of the n(n1)2\frac{n(n-1)}{2} points of intersection of these lines, kk coins are placed. Ana and Beto play the following game in turns: each player, in turn, chooses one of those points that does not share one of the nn lines with the point chosen immediately before by the other player, and removes a coin from that point. Ana starts and can choose any point. The player who cannot make his move loses. Determine based on nn and kk who has a winning strategy.