Tuesday, October 02, 2007

Bishop Swap Puzzle

As one final tribute to the 7th Guest chess puzzles, I've added the Bishop Swap Puzzle


Summary of Puzzle Experience

Each of these puzzles had unique problems which were fun to work out and gained in complexity (though each whole puzzle only took a couple hours to code, so they weren't terribly complex).

  • The 8 Queens Puzzle wasn't moving any pieces, so I could just put the queen wherever the user clicked. The only complexity was to check for conflicting queens in all directions and remove them. Of course, my initial goal wasn't to make an interactive game, but a solution generator so my wife's move selection strategy was key, but very simple to implement.

  • The Knight Puzzle added the animation for user moves which was more visually interesting. However, since there's only one open square, you don't have to worry about multiple moves for any given piece. The piece can either be moved to the open square or it can't. There were two interesting algorithms necessary for the knight puzzle. The first is pretty simple and is just the computation of valid "L" shaped moves which is done taking the absolute value of the differences of the coordinates of the piece to move and the blank square. If the absolute value of the differences is 1 & 2 (or 2 & 1), then it's valid.
    The second algorithm is a little more interesting. It is how to determine if all the pieces are in the correct location. For this, I added a little weighting of the row and column indicies as follows:
    • let the computedValue = (row * 2) + (column * 3)

    • not done if:
      • any white knights have a computedValue > 10

      • any black knights have a computedValue < 10

      • any piece has a computedValue == 10

    The following matrix demonstrates this:


  • The Bishop Puzzle added the potential of multiple moves for any given bishop selection. So, I had to keep track of what piece was selected, determine which possible moves were available, and when multiple moves are available, highlight them and allow the user to select one.