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#!/usr/bin/env perl
# Challenge 049
#
# TASK #2
# LRU Cache
# Write a script to demonstrate LRU Cache feature. It should support operations
# get and set. Accept the capacity of the LRU Cache as command line argument.
#
# Definition of LRU: An access to an item is defined as a get or a set operation
# of the item. �Least recently used� item is the one with the oldest access time.
#
# For example:
#
# capacity = 3
# set(1, 3)
# set(2, 5)
# set(3, 7)
#
# Cache at this point:
# [Least recently used] 1,2,3 [most recently used]
#
# get(2) # returns 5
#
# Cache looks like now:
# [Least recently used] 1,3,2 [most recently used]
#
# get(1) # returns 3
#
# Cache looks like now:
# [Least recently used] 3,2,1 [most recently used]
#
# get(4) # returns -1
#
# Cache unchanged:
# [Least recently used] 3,2,1 [most recently used]
#
# set(4, 9)
#
# Cache is full, so pushes out key = 3:
# [Least recently used] 2,1,4 [most recently used]
#
# get(3) # returns -1
use Modern::Perl;
{
package Cache;
use Object::Tiny::RW qw( capacity cache );
sub new {
my($class, %args) = @_;
return bless {cache=>[], %args}, $class;
}
sub as_string {
my($self) = @_;
my $out = "";
for (@{$self->cache}) {
$out .= "(".$_->[0]."=>".$_->[1].")";
}
return $out;
}
sub get {
my($self, $k) = @_;
for my $i (0 .. @{$self->cache}-1) {
if ($self->cache->[$i][0] == $k) {
my $v = $self->cache->[$i][1];
splice(@{$self->cache}, $i, 1);
push @{$self->cache}, [$k=>$v];
shift @{$self->cache} while @{$self->cache} > $self->capacity;
return $v;
}
}
return -1;
}
sub set {
my($self, $k, $v) = @_;
my $found = $self->get($k);
if ($found == -1) {
push @{$self->cache}, [$k=>$v];
shift @{$self->cache} while @{$self->cache} > $self->capacity;
}
else {
$self->cache->[-1][1] = $v;
}
}
}
say "Create cache, capacity=>3";
my $cache = Cache->new(capacity=>3);
say "Cache=", $cache->as_string;
say "Set cache:1,3";
$cache->set(1, 3);
say "Cache=", $cache->as_string;
say "Set cache:2,5";
$cache->set(2, 5);
say "Cache=", $cache->as_string;
say "Set cache:3,7";
$cache->set(3, 7);
say "Cache=", $cache->as_string;
say "Get cache 2=>",$cache->get(2);
say "Cache=", $cache->as_string;
say "Get cache 1=>",$cache->get(1);
say "Cache=", $cache->as_string;
say "Get cache 4=>",$cache->get(4);
say "Cache=", $cache->as_string;
say "Set cache:4,9";
$cache->set(4, 9);
say "Cache=", $cache->as_string;
say "Get cache 3=>",$cache->get(3);
say "Cache=", $cache->as_string;
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