A guessing game on polygon and lines
Source: MEMO 2024 I2
August 26, 2024
combinatoricscombinatorial geometrypolygonquestionguessing game
Problem Statement
There is a rectangular sheet of paper on an infinite blackboard. Marvin secretly chooses a convex -gon that lies fully on the piece of paper. Tigerin wants to find the vertices of . In each step, Tigerin can draw a line on the blackboard that is fully outside the piece of paper, then Marvin replies with the line parallel to that is the closest to which passes through at least one vertex of . Prove that there exists a positive integer , independent of the choice of the polygon, such that Tigerin can always determine the vertices of in at most steps.