Mr. Shawn H. Corey wrote:
> Mr. Shawn H. Corey wrote:
>
>>Your solution will only work if $element is unique. Otherwise you will
>>have multiple copies of $element on the list, and not the $maximum
>>(unique) number of items.
>>
>>Try:
>>
>> @recent = grep { ! /^$element$/ } @recent;
>> unshift @recent, $element;
>> $#recent = $maximum;
>>
>>Notice how things became even slower?
>>
>>
>
>
> OK, here's a solution that might be faster. The problem with it is
> as_array() which has to scan the list every time. There is not simpler
> way for it to work.
>
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> my $maximum = 20; # minimum maximum == 2
> my $head = 0;
> my $tail = 0;
> my %unique = ();
> my $count = 0;
>
> sub add_element {
> my $element = shift @_;
> my $node = {
> next => 0,
> back => 0,
> data => $element,
> };
>
> if( exists $unique{$element} ){
> if( $unique{$element} eq $head ){
> $head = $unique{$element}->{next};
> }else{
> $unique{$element}->{back}->{next} = $unique{$element}->{next};
> }
> if( $unique{$element} eq $tail ){
> $tail = $unique{$element}->{back};
> }else{
> $unique{$element}->{next}->{back} = $unique{$element}->{back};
> }
> }
>
> if( ref( $head )){
> $node->{next} = $head;
> $head->{back} = $node;
> }else{
> $tail = $node;
> }
> $head = $node;
>
> $unique{$element} = $node;
> $count ++;
>
> if( $count > $maximum ){
> my $item = $tail->{data};
> $tail = $tail->{back};
> $tail->{next} = 0;
> delete $unique{$item};
# Oops, forgot a line:
$count = $maximum;
> }
> }
>
> sub as_array {
> my @array = ();
> my $node = $head;
>
> while( ref( $node )){
> push @array, $node->{data};
> $node = $node->{next};
> }
>
> return @array;
> }
>
> for my $n ( qw( a b c b a a b c d e f g h i j k l m n o p q r s t u v w
> x y z ) ){
> add_element( $n );
> print join( " ", as_array ), "\n";
> }
>
>
>
--
__END__
Just my 0.00000002 million dollars worth,
--- Shawn
"For the things we have to learn before we can do them, we learn by
doing them."
Aristotle
* Perl tutorials at http://perlmonks.org/?node=Tutorials
* A searchable perldoc is at http://perldoc.perl.org/
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