Friday Puzzler -- Checkers

Example

Alex Y

Just to clarify, here is a solution that fails because the last move includes two of the same color. Using numbers to be able to track the movements.

░░░░12345

45░░123░░

4512░░3░░

░░12453░░

53124░░░░

Re: Friday Puzzler -- Checkers

Larry Barrett

I think you can do it in 4 moves.

Very good

Alex Y

Give a couple of days in case ohers want to work on it, knowing how many moves it takes, then post your solution AND HOW YOU WORKED IT OUT. It is always interesting to know the how.

Solution

Larry Barrett

Here is my solution (the dashes don't quite line up with the letters, so you may need to count):

BRBRB------

BR--B--BR--

----B--BRBR

----BRBB--R

------BBBRR

I saw this puzzle about 40 years ago. It may have been a Martin Gardner puzzle, but I 'm not sure now. I solved it backwards from the final position. In that position only the BR pair could have been moved to reach that position, and there are only two places they could have been before that move. Trial and error from there.

This puzzle makes a good bar bet. With a little practice you can make the four moves in about 4 seconds. So you can offer to show someone how to solve this and bet that even if they see it they won't be able to repeat it. (I have not actually tried this out, but seems like it might work.)

Re: Solution

Alex Y

I'm impressed that you remembered it from 40 years ago! Yes, it was an MG puzzle. Working backwards as you did is the best way I know to attack it, and trial and error after the first backwards move.