MathDB
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 20222022 steps; the steps are listed 11, 22, ...... , 20222022 and the floor is considered step 00. 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 77 steps, that is, if they are in the steps mm andn n, then it must always be true that mn7|m-n| \le 7. 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 nn-th step, then on the next turn the other player cannot be moved to any of the steps n1n-1, nn or n+1n + 1, except when it is for reach the last step. d) Whoever reaches the last step (listed with 20222022) wins. Shikamaru is bored to start, so his father starts. Determine which of the two players has a winning strategy and describe it.