MathDB
JBMO Shortlist 2022 C1

Source: JBMO Shortlist 2022

June 26, 2023
combinatoricsgameJuniorBalkanshortlist

Problem Statement

Anna and Bob, with Anna starting first, alternately color the integers of the set S={1,2,...,2022}S = \{1, 2, ..., 2022 \} red or blue. At their turn each one can color any uncolored number of SS they wish with any color they wish. The game ends when all numbers of SS get colored. Let NN be the number of pairs (a,b)(a, b), where aa and bb are elements of SS, such that aa, bb have the same color, and bāˆ’a=3b - a = 3. Anna wishes to maximize NN. What is the maximum value of NN that she can achieve regardless of how Bob plays?