MathDB
Pebble Game

Source: KöMaL A. 790

March 24, 2022
combinatoricswinning strategykomal

Problem Statement

Andrew and Barry play the following game: there are two heaps with aa and bb pebbles, respectively. In the first round Barry chooses a positive integer k,k, and Andrew takes away kk pebbles from one of the two heaps (if kk is bigger than the number of pebbles in the heap, he takes away the complete heap). In the second round, the roles are reversed: Andrew chooses a positive integer and Barry takes away the pebbles from one of the two heaps. This goes on, in each round the two players are reversing the roles. The player that takes the last pebble loses the game.
Which player has a winning strategy?
Submitted by András Imolay, Budapest