PHP实现双向链表的一例代码

/**
 * **双向链表
 * @author zhiyuan12@
 * @modified 2012-10-25
 * @site: bbs.it-home.org
 */
/**
 * 链表元素结点类
 */
class Node_Element {
    public $pre = NULL; // 前驱
    public $next = NULL; // 后继
    public $key = NULL; // 元素键值
    public $data = NULL; // 结点值
    function __Construct($key, $data) {
        $this->key = $key;
        $this->data = $data;
    }
}
/**
 * 双向链表类
 */
class DoubleLinkedList {
    private $head; // 头指针
    private $tail; // 尾指针
    private $current; // 当前指针
    private $len; // 链表长度
    function __Construct() {
        $this->head = self::_getNode ( null, null );
        $this->curelement = $this->head;
        $this->tail = $this->head;
        $len = 0;
    }
    /**
     * @ desc: 读取链表全部结点
     */
    public function readAll() {
        $tmp = $this->head;
        while ( $tmp->next !== null ) {
            $tmp = $tmp->next;
            var_dump ( $tmp->key, $tmp->data );
        }
    }
    public function move($pos1, $pos2) {
        $pos1Node = $this->findPosition ( $pos1 );
        $pos2Node = $this->findPosition ( $pos2 );
        if ($pos1Node !== null && $pos2Node !== null) {
            $tmpKey = $pos1Node->key;
            $tmpData = $pos1Node->data;
            $pos1Node->key = $pos2Node->key;
            $pos1Node->data = $pos2Node->data;
            $pos2Node->key = $tmpKey;
            $pos2Node->data = $tmpData;
            return true;
        }
        return false;
    }
    /**
     * @ desc: 在指定关键词删除结点
     *
     * @param : $key
     *          指定位置的链表元素key
     */
    public function delete($key) {
        $pos = $this->find ( $key );
        if ($pos !== null) {
            $tmp = $pos;
            $last = null;
            $first = true;
            while ( $tmp->next !== null && $tmp->next->key === $key ) {
                $tmp = $tmp->next;
                if (! $first) {
                    $this->delNode ( $last );
                } else {
                    $first = false;
                }
                $last = $tmp;
            }
            if ($tmp->next !== null) {
                $pos->pre->next = $tmp->next;
                $tmp->next->pre = $pos->pre;
            } else {
                $pos->pre->next = null;
            }
            $this->delNode ( $pos );
            $this->delNode ( $tmp );
        }
    }
    /**
     * @ desc: 在指定位置删除结点
     *
     * @param : $key
     *          指定位置的链表元素key
     */
    public function deletePosition($pos) {
        $tmp = $this->findPosition ( $pos );
        if ($tmp === null) {
            return true;
        }
        if ($tmp === $this->getTail ()) {
            $tmp->pre->next = null;
            $this->delNode ( $tmp );
            return true;
        }
        $tmp->pre->next = $tmp->next;
        $tmp->next->pre = $tmp->pre;
        $this->delNode ( $tmp );
    }
    /**
     * @ desc: 在指定键值之前插入结点
     *
     * @param : $key
     *          //指定位置的链表元素key
     * @param : $data
     *          //要插入的链表元素数据
     * @param : $flag
     *          //是否顺序查找位置进行插入
     */
    public function insert($key, $data, $flag = true) {
        $newNode = self::_getNode ( $key, $data );
        $tmp = $this->find ( $key, $flag );
        if ($tmp !== null) {
            $newNode->pre = $tmp->pre;
            $newNode->next = $tmp;
            $tmp->pre = $newNode;
            $newNode->pre->next = $newNode;
        } else {
            $newNode->pre = $this->tail;
            $this->tail->next = $newNode;
            $this->tail = $newNode;
        }
        $this->len ++;
    }
    /**
     * @ desc: 在指定位置之前插入结点
     *
     * @param : $pos
     *          指定插入链表的位置
     * @param : $key
     *          指定位置的链表元素key
     * @param : $data
     *          要插入的链表元素数据
     */
    public function insertPosition($pos, $key, $data) {
        $newNode = self::_getNode ( $key, $data );
        $tmp = $this->findPosition ( $pos );
        if ($tmp !== null) {
            $newNode->pre = $tmp->pre;
            $newNode->next = $tmp;
            $tmp->pre = $newNode;
            $newNode->pre->next = $newNode;
        } else {
            $newNode->pre = $this->tail;
            $this->tail->next = $newNode;
            $this->tail = $newNode;
        }
        $this->len ++;
        return true;
    }
    /**
     * @ desc: 根据key值查询指定位置数据
     *
     * @param : $key
     *          //指定位置的链表元素key
     * @param : $flag
     *          //是否顺序查找
     */
    public function find($key, $flag = true) {
        if ($flag) {
            $tmp = $this->head;
            while ( $tmp->next !== null ) {
                $tmp = $tmp->next;
                if ($tmp->key === $key) {
                    return $tmp;
                }
            }
        } else {
            $tmp = $this->getTail ();
            while ( $tmp->pre !== null ) {
                if ($tmp->key === $key) {
                    return $tmp;
                }
                $tmp = $tmp->pre;
            }
        }
        return null;
    }
    /**
     * @ desc: 根据位置查询指定位置数据
     *
     * @param : $pos
     *          //指定位置的链表元素key
     */
    public function findPosition($pos) {
        if ($pos  $this->len)
            return null;
        if ($pos len / 2 + 1)) {
            $tmp = $this->head;
            $count = 0;
            while ( $tmp->next !== null ) {
                $tmp = $tmp->next;
                $count ++;
                if ($count === $pos) {
                    return $tmp;
                }
            }
        } else {
            $tmp = $this->tail;
            $pos = $this->len - $pos + 1;
            $count = 1;
            while ( $tmp->pre !== null ) {
                if ($count === $pos) {
                    return $tmp;
                }
                $tmp = $tmp->pre;
                $count ++;
            }
        }
        return null;
    }
    /**
     * @ desc: 返回链表头节点
     */
    public function getHead() {
        return $this->head->next;
    }
    /**
     * @ desc: 返回链表尾节点
     */
    public function getTail() {
        return $this->tail;
    }
    /**
     * @ desc: 查询链表节点个数
     */
    public function getLength() {
        return $this->len;
    }
    private static function _getNode($key, $data) {
        $newNode = new Node_Element ( $key, $data );
        if ($newNode === null) {
            echo "new node fail!";
        }
        return $newNode;
    }
    private function delNode($node) {
        unset ( $node );
        $this->len --;
    }
}
// $myList = new DoubleLinkedList ();
// $myList->insert ( 1, "test1" );
// $myList->insert ( 2, "test2" );
// $myList->insert ( "2b", "test2-b" );
// $myList->insert ( 2, "test2-c" );
// $myList->insert ( 3, "test3" );
// $myList->insertPosition ( 5, "t", "testt" );
// $myList->readAll ();
// echo "+++";
// $myList->deletePosition(0);
// $myList->readAll ();
// echo "..." . $myList->getLength ();
// var_dump ( $myList->findPosition ( 3 )->data );
?>