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Perl: the Markov chain saw

Re: sort with fewest moves

by jlongino (Parson)
on Feb 10, 2002 at 17:21 UTC ( [id://144477] : note . print w/replies, xml ) Need Help??

in reply to sort with fewest moves

If this were homework (but of course it's not), I imagine a teacher would be very impressed if one of their students developed a uniquely Perl solution. Instead of trying to move elements around one at a time, come up with an algorithm to swap at least two elements.

For example, with Perl you could solve this specific problem with the following two statements:

($slots[1], $slots[2]) = ($slots[2], $slots[1]); ($slots[2], $slots[3]) = ($slots[3], $slots[2]);
and, of course, with one statement:
($slots[1], $slots[2], $slots[3]) = ($slots[2], $slots[3], $slots[1]);
Coming up with an algorithm for two in-place swaps shouldn't be too difficult (I've already shown you the Perl idiom), ++ if you can handle more than two elements at a time.


Update: Well, that's the algorithm part I alluded to, your list of moves for the 2-element swap would look like this:

  • swap(1, 2)
  • swap(2, 3)
Granted trying to notate a 3 at-a-time swap would be difficult, if even possible (thus the ++).

If we'd known that you had to use a one-armed robot to begin with, the replies might have been more useful. ;)

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Re: Re: sort with fewest moves
by axelrose (Scribe) on Feb 10, 2002 at 19:25 UTC
    Do you mean something like
    @slots = @slots[2,1,4,3]
    It looks nice but I really need a list of move actions for the robot.