Building Nim

TL;DR

Building Nim is a two-stage game combining token placement and Nim gameplay, with solutions and conjectures provided for specific cases, exploring strategic placement to avoid Nim-sum zero.

Contribution

The paper introduces Building Nim, a new variation of Nim with a building phase, and offers solutions for certain cases along with a general conjecture.

Findings

Solution for some non-trivial cases of Building Nim.

Identification of trivial cases based on token and stack counts.

Formulation of a general conjecture for the game.

Abstract

The game of nim, with its simple rules, its elegant solution and its historical importance is the quintessence of a combinatorial game, which is why it led to so many generalizations and modifications. We present a modification with a new spin: building nim. With given finite numbers of tokens and stacks, this two-player game is played in two stages (thus belonging to the same family of games as e.g. nine-men's morris): first building, where players alternate to put one token on one of the, initially empty, stacks until all tokens have been used. Then, the players play nim. Of course, because the solution for the game of nim is known, the goal of the player who starts nim play is a placement of the tokens so that the Nim-sum of the stack heights at the end of building is different from 0. This game is trivial if the total number of tokens is odd as the Nim-sum could never be 0, or if both the number of tokens and the number of stacks are even, since a simple mimicking strategy results in a Nim-sum of 0 after each of the second player's moves. We present the solution for this game for some non-trivial cases and state a general conjecture.