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

(In reply to Confusing by jduval)

Extracted from John's comment;

"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.

No, I was fully aware of what Hugo was saying.  I saw no problem with the definition of a 'move'.  My intent was to clarify succinct for myself; I could envisage also a set of solutions being posted where that instruction was misread.

Sometimes it helps to add to the problem if you have to sort out the meaning of what is written.  When I began with the N-frog puzzle, Hugo's "Jump Around". I had trouble with the frog changing its identity. I didn't dwell on it so I didn't realise the meaning until I saw the solution of Tiralmo.

No, I found the instruction here quite clear.

Edited on July 12, 2005, 5:28 am

Posted by brianjn on 2005-07-12 05:24:52