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Treebeard's Stumper
17 January 2003

Peaceful Knights

We're having our Dunn Middle School Waffles 'N Jammies chess tournament today, so here's an ancient chess stumper to play between games. Start with any 3 by 3 part of a chessboard. Place two white knights in the upper corner squares and two black knights in the lower corners. The stumper is to swap the white and black knights in the fewest possible moves. Of course they must make the usual knight moves, and only one peaceful knight can be on a square at a time. If that's too easy, then what is the smallest size board you need to exchange three (or more) knights on each side?

I call this stumper "Peaceful Knights" because only one knight can be on a square at a time, and there are no captures or kills allowed in this peaceful solitaire game. It's also appropriate because Monday, January 20, 2003 is Dr. Martin Luther King, Jr. Day. It is a good time to make a personal stand for effective non-violence when it's needed. It's a basic rule of computer programming (and life) that there is always another way!

A move is a move, and there is a minimum number required. It's more challenging if you count one play as moving a single piece through succesive moves until stopped by the rules. What is the smallest number of plays that can solve this stumper? Exchanging three or more pieces on each side (and recording the moves) is a real stumper!

Answer


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Copyright © 2003 by Marc Kummel / mkummel@rain.org