PHP实现LRU算法的原理详解

<?php
class Node
{
    public $preKey = null; //链表前一个节点
    public $nextKey = null;  //链表后一个节点
    public $key= null;      //当前的值
    public $value= null;    //当前key

    public function __construct($key,$value){
        $this->key = $key;
        $this->value = $value;
    }

    public function setPre($preKey)
    {
        $this->preKey = $preKey;
    }

    public function setNext($nextKey)
    {
        $this->nextKey = $nextKey;
    }
}

class LRUCache{
    public $cacheTable = [];
    /** Node null  */
    private $headNode = null;
    private $lastNode = null;
    private $cacheCount = 0;
    private $cacheMax = 3;

    public function addNode($key,$value)  //此处采用头插法
    {
        $addNode = new Node($key,$value);
        if ( !empty($this->headNode))
        {
            $this->headNode->preKey = $addNode; //如果链表存在，将节点添加到节点前一个
        }
        $addNode->nextKey = $this->headNode;

        //第一次保存最后一个节点为头结点
        if ($this->lastNode == null){
            $this->lastNode = $addNode;
        }

        $this->headNode = $addNode;
        $this->cacheTable[$key] = $addNode;
        $this->cacheCount++;

    }

    public function set($key,$value)
    {
        //先判断是否需要删除
        $this->shiftNode();
        $this->addNode($key,$value);
        return true;
    }

    //自动删除
    public function shiftNode()
    {
        while ($this->cacheCount >= $this->cacheMax){
            if (!empty($this->lastNode)){
                if ($this->lastNode->preKey){
                    $this->lastNode->preKey->nextKey = null;
                    $this->lastNode = $this->lastNode->preKey;
                }

                unset($this->cacheTable[$this->lastNode->key]);
            }
            $this->cacheCount --;
        }
    }

    public function dumpAllData()
    {
        $node = $this->headNode;
        while (($node)){
            echo "key=".$node->key."value=".$node->value."\n";
            $node = $node->nextKey;
        }
    }

}


$Cache = new LRUCache();
$Cache->set("a","aaaaaaaaaaa");
$Cache->set("b","bbbbbbbbbbb");
$Cache->set("c","ccccccccccc");
$Cache->set("d","dddddddddddd");
$Cache->set("e","eeeeeeeeeeee");
//$Cache->set("f","ffffffffffff");
$Cache->dumpAllData();
//var_dump($Cache);  //是一个深度的数组（对象）