Andrea Holstein wrote:
>
> "John W. Krahn" wrote:
>
> > That looks like a direct translation of algorithm 5.2.2B from TAoCP Vol.
> > 3 however the usual implementation is more like Sedgewick's example:
> >
> > sub bubble {
> > my $a = shift;
> >
> > for ( my $i = @$a; $i >= 1; $i-- ) {
> > for ( my $j = 2; $j <= $i; $j++ ) {
> > if ( $a->[ $j - 1 ] > $a->[ $j ] ) {
> > $a->[ $j - 1, $j ] = $a->[ $j, $j - 1 ];
> > }
> > }
> > }
> > }
> >
> Oh my dear, that's really unperlish :-)
That's because Sedgewick's book is titled _Algorithms in C_
> What do you think of:
>
> sub bubble {
> my $a = shift;
> my @a = @$a;
You make a copy of the array, could be very expensive.
> foreach my $i (reverse (1 .. @a)) {
> foreach my $j (2 .. $i) {
> ($a[$j-1], $a[$j]) = ($a[$j], $a[$j-1]) if $a[$j-1] > $a[$j];
> }
> }
> return $a;
You return the reference to the original array (which hasn't been
modified.) So basicly you sort a copy of an array and then throw it
away.
> }
>
> Note, that I changed the assignment, too, so now it should work :-)
Yes, sorry, it should have been:
@$a[ $j - 1, $j ] = @$a[ $j, $j - 1 ];
John
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