## 24 Knight Swap

 Puzzle 1 ```+---+---+---+---+---+ | B | B | B | W | W | 1 +---+---+---+---+---+ | B | B | B | W | W | 2 +---+---+---+---+---+ | B | B | | W | W | 3 +---+---+---+---+---+ | B | B | W | W | W | 4 +---+---+---+---+---+ | B | B | W | W | W | 5 +---+---+---+---+---+ a b c d e ``` ` ` Puzzle 2 ```+---+---+---+---+---+ | B | B | B | B | W | 1 +---+---+---+---+---+ | B | B | B | W | W | 2 +---+---+---+---+---+ | B | B | | W | W | 3 +---+---+---+---+---+ | B | B | W | W | W | 4 +---+---+---+---+---+ | B | W | W | W | W | 5 +---+---+---+---+---+ a b c d e ```
1. Place 12 black and 12 white knights in a 5x5 grid, with the center square unoccupied. Place blacks left and above the center square and whites right and below the center square. Swap the colors in as few moves as possible.
2. Puzzle 2 is the actual original puzzle I was sent. I misread the description, so I just decided to make it a second puzzle. It differs from the first by one square, making more of a triangular arrangement of the knights.
Source: A reader, citing Zillions of Games's Knight-Swap puzzles. (If anyone has a better source, let me know.)
Update 4/10/01. Al Zimmermann improved upon both solutions. Each of these solutions is computer-generated and is the shortest possible.
```Here's a 40-move solution for the 1st problem:

1b, 2d, 3b, 5c, 4e, 3c, 5d, 4b, 3d, 1c,
2a, 3c, 5b, 4d, 2c, 1a, 3b, 5a, 4c, 5e,
3d, 1c, 2e, 4d, 2c, 1e, 3d, 2b, 4c, 3a,
2c, 3e, 4c, 2d, 3b, 5c, 4a, 2b, 1d, 3c
```
```Here's a 36-move solution to the 2nd problem:

1b, 2d, 3b, 5c, 4e, 3c, 2e, 1c, 3d, 2b,
4c, 5e, 3d, 4b, 2a, 3c, 1d, 3e, 2c, 1a,
3b, 5a, 4c, 3a, 5b, 3c, 4a, 5c, 3b, 4d,
2c, 1e, 3d, 4b, 5d, 3c```

These solutions were received from Colin Bown.
1. ```This may not be minimum but it gets the job done in 64 moves.

5d, 4b, 3d, 1c, 2e, 4d, 2c, 3e, 1d, 2b,
4c, 1a, 5d, 4b, 3d, 1c, 2e, 4d, 2c, 3e,
1d, 2b, 4c, 3a, 5b, 3c, 1b, 2d, 3b, 5c,
4a, 3c, 4e, 5c, 4a, 3c, 2a, 1c, 2e, 3c,
5d, 3e, 1d, 3c, 5d, 3e, 4c, 3a, 2c, 1e,
3d, 5e, 4c, 5a, 3b, 1a, 2c, 4b, 3d, 5c,
3b, 1c, 2a, 3c```
2. ```Here's a 46 move solution to part 2:

5d 4b 3d 1c 2e 4d 2c 3e 1d 3c
1b 2d 3b 5c 4a 2b 4c 3a 5b 3c
4e 5c 4a 3c 2a 1c 2e 3c 5d 3e
4c 5a 3b 1a 2c 1e 3d 5e 4c 2d
3b 1c 3d 5c 4e 3c```
Thanks to Al Zimmermann for checking these solutions.
Mail to Ken