The numeric keyboards of a telephone (left) and a pocket calculator (right) differ in the arrangement of the keys.

123   789
456   456
789   123
  0      0

What is the least number of moves necessary to transfer the keys of the first arrangement into the other arrangement?
One move consists of switching the position of two neighbouring keys (Horizontal, vertical or diagonal) of which the sum is 9, 10 or 11.
Example: In the starting position you can switch 6 and 3, 5 and 6, 4 and 5, 7 and 4, 0 and 9

The problem wording is a little confusing.  I believe you are defining a move in sentence two but that is not completely clear.  If that is what you are defining as the only legal move, it should be stated clearer.  "One move consists" could be read as one 'such' move, or one 'possible' move, suggesting that there are other possible moves.  I believe brianjn initially came to the same conclusion as is apparent in his first post.  Only in reading the comment string was I able to figure out that you were defining a move in the second sentence and not suggesting a possible move. 

It is a good problem however.  Unfortunately it does not hold my interest enough to solve it.  So I would also have to agree with "uninterresting".  Although that is my opinion and does not make it a bad problem.  I am rating it a 3, a combination of the quality of the problem and my interest level.

Posted by john on 2005-07-07 16:00:42