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

I analyzed (many times) the solution presented by Leming, searching where I could make something different to obtain a certain position that he achieved.

So, this reduction is totally based on Leming´s solution, who deserves, more than me, the credit of solving this excellent puzzle.

Posted by pcbouhid on 2005-07-26 15:10:07