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Alice and Bob move tile around a n-gon, who will win?

Source: Francophone 2024, Junior P2

April 4, 2024
combinatoricscombinatorics proposedgamewinning strategy

Problem Statement

Given n2n \ge 2 points on a circle, Alice and Bob play the following game. Initially, a tile is placed on one of the points and no segment is drawn. The players alternate in turns, with Alice to start. In a turn, a player moves the tile from its current position PP to one of the n1n-1 other points QQ and draws the segment PQPQ. This move is not allowed if the segment PQPQ is already drawn. If a player cannot make a move, the game is over and the opponent wins. Determine, for each nn, which of the two players has a winning strategy.