MathDB
2 player game drawing segments of length 1

Source: 2023 Austrian Federal Competition For Advanced Students, Part 2 p3

May 17, 2024
combinatoricsgeometrycombinatorial geometry

Problem Statement

Alice and Bob play a game, in which they take turns drawing segments of length 11 in the Euclidean plane. Alice begins, drawing the first segment, and from then on, each segment must start at the endpoint of the previous segment. It is not permitted to draw the segment lying over the preceding one. If the new segment shares at least one point - except for its starting point - with one of the previously drawn segments, one has lost. a) Show that both Alice and Bob could force the game to end, if they don’t care who wins. b) Is there a winning strategy for one of them?