PHP实现链表结构

<?php

//结点类
class node { 
    
    public $data;
    public $next;
    
    function __construct($data) {
        $this->data = $data;
        $this->next = null;
    }
}

//链表类，链表中所有结点位置标号从1起始
class linkList {
    
    //头结点
    private $header;
        
    function __construct () {
        $this->header = new node(null);
    }
    
    /**
     * 判断链表是否为空
     * @return bool
     */
    function isEmpty() {
        return ($this->header->next == null);
    }
    
    /**
     * 返回链表长度
     * @return int
     */
    function getLength() {
        $len = 0;
        $link = $this->header;
        while($link->next != null)
        {
            $len++;
            $link = $link->next;
        }
        return $len;
    }
    
    /**
     * 返回链表中值为$data的结点位置
     * @return array(找到结点)  false(未找到结点)
     */
    function find($data) {
        $index = array();
        $pos = 0;
        $link = $this->header;
        while($link != null)
        {
            if($link->data === $data) {
                $index[] = $pos;
            }
            $pos++;
            $link = $link->next;
        }
        if(count($index) == 0) $index = false;
        return $index;
    }
    
    /**
     * 在链表第$index个位置插入值为$data的结点
     * @return bool
     */
    function insertAt($index, $data) {
        if(($index > $this->getLength()) || ($index < 1))
            return false;
        $link = $this->header;
        $pos = 0;
        while($index != $pos) {
            $prev = $link;
            $pos++;
            $link = $link->next;
        }
        $new = new node($data);
        $prev->next = $new;
        $new->next = $link; 
        return true;
    }
    
    /**
     * 在链表末尾添加值为$data的结点
     */
    function append($data) {
        $link = $this->header;
        while($link->next != null)
        {
            $link = $link->next;
        }
        $link->next = new node($data);        
    }
    
    /**
     * 删除链表第$index个结点
     * @return $deleted 删除结点的值
     */
    function deleteAt($index) {
        if(($index > $this->getLength()) || ($index < 1))
            return false;
        $link = $this->header;
        $pos = 0;
        while($pos != $index) {
            $prev = $link;
            $pos++;
            $link = $link->next;
        }
        $prev->next = $link->next;
        $deleted = $link->data;
        unset($link);
        return $deleted;
    }
    
    /**
     * 删除链表中所有值为$data的结点
     */
    function deleteIs($data) {
        $link = $this->header;
        while($link != null) {
            if($link->data !== $data) {
                $prev = $link;
                $link = $link->next;
            }
            else {
                $prev->next = $link->next;
                unset($link);
                $link = $prev->next;
            }
        }
    }
    
    /**
     * 更新链表第$index个结点的值为$data
     * @return $updated 更新前的值
     */
    function updateAt($index, $data) {
        if(($index > $this->getLength()) || ($index < 1))
            return false;
        $link = $this->header;
        $pos = 0;
        while($pos != $index) {
            $pos++;
            $link = $link->next;
        }
        $updated = $link->data;
        $link->data = $data;
        return $updated;
    }
    
    /**
     * 将链表中所有值为$old的结点值替换为$new
     */
    function replace($old, $new) {
        $link = $this->header;
        while($link != null) {
            if($link->data === $old) {
                $link->data = $new;
            }
            $link = $link->next;
        }
    }
    
    /**
     * 销毁链表
     */
    function destroy() {
        $this->header->next = null;
    }
    
    /**
     * 清空链表
     * 保留链表长度，令链表中每个结点为值为NULL
     */
    function truncate() {
        $link = $this->header;
        while($link != null)
        {
            $link->data = null;
            $link = $link->next;
        }
    }

    /**
     * 显示链表信息
     */
    function display() {
        if($this->isEmpty()) {
            echo "This is an empty linklist!\n";
            return;
        }
        
        $len = $this->getLength();
        if($len > 1)
            $msg = "There are {$len} elements in this linklist:\n";
        else
            $msg = "There is only 1 element in this linklist:\n";
        echo $msg;
        $i = 1;
        $link = $this->header;
        while($link->next != null) {
            $link = $link->next;
            printf("Data %02d is %s\n",$i,$link->data);
            $i++;
        }
    }

}

$testList = new linkList();
for($i=0;$i<20;$i++) {
    $testList->append(chr(ord('A') + rand(0,25)));
}
$testList->display();
$element = 'B';
printf("Searching for Element %s ...\n",$element);
if(false !== ($pos = $testList->find($element))) {
    for($i=0;$i<count($pos);$i++)
        printf("Data %02d is %s\n",$pos[$i],$element);
}
else {
    printf("Element %s is not found!\n",$element);
}
$testList->insertAt(2,'Z');
$testList->display();
$testList->updateAt(4,'G');
$testList->display();
$testList->deleteAt(6);
$testList->display();
$testList->replace('N','B');
$testList->display();
$testList->deleteIs('B');
$testList->display();
$testList->destroy();
$testList->append('X');
$testList->display();

?>