MathDB
Apples on a tree

Source: 2023 Israel Olympic Revenge P1

June 15, 2023
olympic revengecombinatoricsgraph theory

Problem Statement

Armadillo and Badger are playing a game. Armadillo chooses a nonempty tree (a simple acyclic graph) and places apples at some of its vertices (there may be several apples on a single vertex). First, Badger picks a vertex v0v_0 and eats all its apples. Next, Armadillo and Badger take turns alternatingly, with Armadillo starting. On the ii-th turn the animal whose turn it is picks a vertex viv_i adjacent to vi1v_{i-1} that hasn't been picked before and eats all its apples. The game ends when there is no such vertex viv_i.
Armadillo's goal is to have eaten more apples than Badger once the game ends. Can she fulfill her wish?