Re: Re: Algorithm Pop Quiz: Sorting

[Jasper]

I knocked together an almost identical bit of code, apart from the gt bit, which really is the same:

sub sort_stack {

  local $depth = pop @stack;
  local $sort_depth = $depth;

  for (1..$depth) {
    for (1..$sort_depth) {

      local $top  = pop @stack;
      local $next = pop @stack;

      if ($top gt $next) {

        $top  ^= $next;
        $next ^= $top;
        $top  ^= $next;

      }
      push @stack, $next, $top;
      rotate_up($sort_depth);
    }

    rotate_up($sort_depth);
    --$sort_depth;
  }
  push @stack, $depth;
}

Although I hadda go and use an xor swap, to make it look quite cool..

[RMGir]

Sure, it looks cool. It's just wrong :)

The problem with xor on strings is it will extend short ones. There are now 0 bytes there that weren't there before, and length changes.

$ perl -e'$a="a"; $b="bbb"; $a^=$b; $b^=$a; $a^=$b; print "/$a/,/$b/\n
+"; print length($a),"\n"; print length($b),"\n"'
/bbb/,/a/
3
3


--
Mike

[Jasper]

Mike, thanks, I think. How odd. I had no idea this happened. That'll teach me. Still, I've never had a computer science lesson in my life, so how am I expected to know these things!?! :) Cheers, Jasper

[RMGir]

Hehe, to tell you the truth, I DO have a CS background, and I never would have known this happened in perl if I hadn't run into the string extension problem using the preserve_case routine from perlfaq6.
--
Mike

[clintp]

BZZZT

I'm going to disallow this one as it's relying on a feature that's language dependent for its implementation (the XOR swap for stings). The sprit is there, but you're starting to wander. This kind of behavior needs to be discouraged early! Use the extra register for the swap. :)

These are all so good though. The excitement is terrible. Just terrible!