Peaceful Rooks:
A peaceful rook moves on a chessboard like a rook, except that when
he comes to another piece, he stops jsut in front of it (instead of
capturing it). Moreover, such rooks always move as far as they can 
along any row and column (until blocked; if they do not run into a 
blocker, they fall off the end of the board).
Starting from the configuration of 7 rooks on a 7x7 board shown, 
find a sequence of moves that moves the rook in the upper left 
to the empty square in the center.

 ---------------------------
| X |   |   |   |   |   | O |
|---------------------------|
|   |   |   |   |   | O |   |
|---------------------------|
|   |   |   |   |   |   |   |
|---------------------------|
|   |   |   |   |   |   |   |
|---------------------------|
|   |   |   |   |   |   |   |
|---------------------------|
|   | O |   |   |   | O |   |
|---------------------------|
| O |   |   |   |   |   | O |
 ---------------------------


Centerpiece (Nob Yoshigarhara):
In the following 7x7 board, there are seven UFO's. Each can move
in any of the four directions, north, east, west and south. Once
it starts moving, it cannot stop unless the next square in its 
path is occupied by another UFO. If it reaches the border of the
board before it is stopped, it simply disappears. The object of
the puzzle is to get the UFO marked X into the center square 
(marked with a dot). Other UFO's can occupy this square temporarily,
eventually moving out to make room for X. Remember that the target
square by itself does not stop a UFO there. 


Sources:
  This type of puzzle was invented by Hiroshi Yamamoto and is now 
  marketed by BinaryArts under the name Lunar Lockout (5x5 board).
  This special constellation is from Nob.

  - Mathematics and Informatics Quarterly, 2001:2, p. 104.
  - Macalester College Problem of the Week 946: Peaceful Rooks
    http://mathforum.org/wagon/  with solution.


References:

- John Rausch;
  Computer Analysis of the UFO Puzzle,
  (Lunar Lockout)
  http://www.johnrausch.com/PuzzleWorld/art/articles.htm
  http://www.johnrausch.com/PuzzleWorld/art/art03.htm   Analysis
  http://www.johnrausch.com/PuzzleWorld/art/art03.pdf
  http://www.johnrausch.com/PuzzleWorld/art/art03s.htm  Supplement
  http://www.johnrausch.com/PuzzleWorld/art/art03s.pdf

- Bob Kirkland;
  Java version,
  http://www.johnrausch.com/PuzzleWorld/app/lunar_lockout/lunar_lockout.htm

- Konstantin Knop;
  (2000)
  http://www.computerra.ru/online/knopki/puzzles/4187/

- Lunar Lockout;
  The puzzle was developed by Hiroshi Yamamoto in 1998 and is 
  marketed by Binary Arts under the name "Lunar Lockout".
  http://www.binaryarts.com/Our%20Products/BA/01p_lunarlockout.htm

- Stan Wagon;
  Macalester College Problem of the Week 946: Peaceful Rooks
  http://mathforum.org/wagon/  with solution.

- Nob Yoshigarhara;
  Centerpiece (Problem GG12.1),
  Goodsell Gazette 19:12 (Jan 2001)
  Mathematics and Computer Science, Carleton College
  http://www.mathcs.carleton.edu/gazette/jan19-01/

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