x and o game, in an infinite grid of regular triangles
Source: Norwegian Mathematical Olympiad 2017 - Abel Competition p3b
September 3, 2019
combinatoricsgamegame strategy
Problem Statement
In an infinite grid of regular triangles, Niels and Henrik are playing a game they made up.
Every other time, Niels picks a triangle and writes in it, and every other time, Henrik picks a triangle where he writes a . If one of the players gets four in a row in some direction (see figure), he wins the game.
Determine whether one of the players can force a victory.
https://cdn.artofproblemsolving.com/attachments/6/e/5e80f60f110a81a74268fded7fd75a71e07d3a.png