OK, here's the early-exit version. This proved more straight-forward than I was expecting. I was so sure that applying the knowledge of last-exchange would be difficult, I overlooked how trivial it actually is.

(This is still a bubble-sort, but it no longer is compelled to iterate [ $length - 1 ] times. Rather, the false-bottom can jump over several iterations if there is a clump of sorted elements at the end. Given the six-element sample list here, it saves only 3 iterations of the inner-loop, 17 versus 20 in my original.)


# Assume that rotate_up as defined in the original problem
# statement has been defined.

sub sordid
{
    local $len = pop(@stack);
    local $bum = $len;

    local ($x, $y, $limit, $last_swap);

    while ($bum > 1)
    {
        $limit = $bum;
        $last_swap = 0;
        while (--$limit)
        {
            $x = pop(@stack);
            $y = pop(@stack);

            if ($x gt $y)
            {
                push(@stack, $x);
                push(@stack, $y);
                $last_swap = $bum - $limit;
            }
            else
            {
                push(@stack, $y);
                push(@stack, $x);
            }

            rotate_up($bum);
        }
        # At end of the $limit loop, top element is the max, and
        # top+1 to end is semi-sorted. One more rotate_up()
        # is needed before moving the floor up one notch.
        rotate_up($bum);
        $bum = $last_swap;
    }

    push(@stack, $len);
}

@stack = qw(d b f a e c 6);  # <-- bottom .. top -->

print "(@stack)\n";
# Prints: (d b f a e c 6)
sordid();
print "(@stack)\n";
# Prints: (f e d c b a 6)

[download]

--rjray

In reply to Improved Bubble-Sort (Re: Re: Algorithm Pop Quiz: Sorting) by rjray
in thread Algorithm Pop Quiz: Sorting by clintp

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