2-player game, staircase with 2022 steps
Source: OLCOMA Costa Rica National Olympiad, Final Round, 2022 p3
March 26, 2024
combinatorics
Problem Statement
Shikaku and his son Shikamaru must climb a staircase that has steps; the steps are listed , , , and the floor is considered step . This bores them both a lot, so so they decide to organize a game. They begin by tying a rope between them, so that At most they can be separated from each other by a distance of steps, that is, if they are in the steps and, then it must always be true that . For the game they establish the following rules:
a) They move alternately in turns.
b) In his corresponding turn, the player must move to a higher step than in the one that (the same) was previously.
c) If a player has just moved to the -th step, then on the next turn the other player cannot be moved to any of the steps , or , except when it is for reach the last step.
d) Whoever reaches the last step (listed with ) wins.
Shikamaru is bored to start, so his father starts. Determine which of the two players has a winning strategy and describe it.