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#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
{ package Linked::List;
use enum qw( KEY VALUE PREV NEXT );
sub new {
my ($class, $key, $value) = @_;
my $self = [];
@$self[KEY, VALUE, PREV, NEXT] = ($key, $value, $self, $self);
bless $self, $class
}
sub extract {
my ($self) = @_;
my $prev = $self->[PREV];
my $next = $self->[NEXT];
$prev->[NEXT] = $next;
$next->[PREV] = $prev;
@$self[PREV, NEXT] = ($self, $self);
}
sub prepend_to {
my ($self, $list) = @_;
return unless $list;
$self->extract if $self->[PREV] != $self;
$self->[NEXT] = $list // $self;
$self->[PREV] = $list->[PREV] // $self;
$list->[PREV][NEXT] = $self;
$list->[PREV] = $self;
}
# Prevent memory leaks.
sub demolish {
$_[0][NEXT] = $_[0][PREV] = undef;
}
sub key { $_[0][KEY] }
sub prev { $_[0][PREV] }
sub next { $_[0][NEXT] }
sub value :lvalue { $_[0][VALUE] }
}
{ package Cache::LRU;
use enum qw( CAPACITY HASH FIRST );
sub new {
my ($class, $capacity) = @_;
my $self = [];
@$self[CAPACITY, HASH, FIRST]
= ($capacity, {}, undef);
bless $self, $class
}
sub get {
my ($self, $key) = @_;
return unless exists $self->[HASH]{$key};
my $element = $self->[HASH]{$key};
if ($element != ($self->[FIRST] // -1)) {
$element->extract;
$element->prepend_to($self->[FIRST]);
$self->[FIRST] = $element;
}
return \$element->value
}
sub set {
my ($self, $key, $value) = @_;
my $element;
if (exists $self->[HASH]{$key}) {
$element = $self->[HASH]{$key};
} else {
$element = 'Linked::List'->new($key, $value);
$self->[HASH]{$key} = $element;
}
$element->prepend_to($self->[FIRST])
unless $element == ($self->[FIRST] // -1);
$self->[HASH]{$key}->value = $value;
$self->[FIRST] = $element;
if (keys %{ $self->[HASH] } > $self->[CAPACITY]) {
my $last = $self->[FIRST]->prev;
$last->extract;
delete $self->[HASH]{ $last->key };
$last->demolish;
}
}
sub inspect {
my ($self) = @_;
my $element = $self->[FIRST];
my @keys;
for (keys %{ $self->[HASH] }) {
unshift @keys, $element->key;
$element = $element->next;
}
return [@keys]
}
}
use Test::More;
my $c = 'Cache::LRU'->new(3);
$c->set(1, 3);
$c->set(2, 5);
$c->set(3, 7);
is_deeply $c->inspect, [1, 2, 3];
is ${ $c->get(2) }, 5, 'get 2';
is_deeply $c->inspect, [1, 3, 2];
is ${ $c->get(1) }, 3, 'get 1';
is_deeply $c->inspect, [3, 2, 1];
is $c->get(4), undef, 'get 4';
is_deeply $c->inspect, [3, 2, 1];
$c->set(4, 9);
is_deeply $c->inspect, [2, 1, 4];
is $c->get(3), undef, 'get 3';
done_testing();
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