用PHP实现的单链表

单链表顾名思义就是一个链式数据结构，它有一个表头，并且除了最后一个节点外，所有节点都有其后继节点。如下图。

首先，我们写出链表节点的类。单链表中的每一个节点，都保存其数据域和后驱指针

//链表节点
class node {
    public $id; //节点id
    public $name; //节点名称
    public $next; //下一节点

    public function __construct($id, $name) {
        $this->id = $id;
        $this->name = $name;
        $this->next = null;
    }
}

链表中还有两个特别重要的方法，插入和删除。插入需要找到插入的位置，把前一个元素的next指针指向被插入的节点，并将被插入节点的next指针指向后一个节点，如下图左侧所示。而删除则是把前一个节点的next指针指向后一个节点，并返回被删除元素的数据内容，如下图右侧所示。
 

//单链表
class singelLinkList {
    private $header; //链表头节点

    //构造方法
    public function __construct($id = null, $name = null) {
        $this->header = new node ( $id, $name, null );
    }

    //获取链表长度
    public function getLinkLength() {
        $i = 0;
        $current = $this->header;
        while ( $current->next != null ) {
            $i ++;
            $current = $current->next;
        }
        return $i;
    }

    //添加节点数据
    public function addLink($node) {
        $current = $this->header;
        while ( $current->next != null ) {
            if ($current->next->id > $node->id) {
                break;
            }
            $current = $current->next;
        }
        $node->next = $current->next;
        $current->next = $node;
    }

    //删除链表节点
    public function delLink($id) {
        $current = $this->header;
        $flag = false;
        while ( $current->next != null ) {
            if ($current->next->id == $id) {
                $flag = true;
                break;
            }
            $current = $current->next;
        }
        if ($flag) {
            $current->next = $current->next->next;
        } else {
            echo "未找到id=" . $id . "的节点！<br>";
        }
    }

    //判断连表是否为空
    public function isEmpty(){
            return $this->header == null;
    }

    //清空链表
    public function clear(){
            $this->header = null;
    }

    //获取链表
    public function getLinkList() {
        $current = $this->header;
        if ($current->next == null) {
            echo ("链表为空!");
            return;
        }
        while ( $current->next != null ) {
            echo 'id:' . $current->next->id . '   name:' . $current->next->name . "<br>";
            if ($current->next->next == null) {
                break;
            }
            $current = $current->next;
        }
    }

    //获取节点名字
    public function getLinkNameById($id) {
        $current = $this->header;
        if ($current->next == null) {
            echo "链表为空!";
            return;
        }
        while ( $current->next != null ) {
            if ($current->id == $id) {
                break;
            }
            $current = $current->next;
        }
        return $current->name;
    }

    //更新节点名称
    public function updateLink($id, $name) {
        $current = $this->header;
        if ($current->next == null) {
            echo "链表为空!";
            return;
        }
        while ( $current->next != null ) {
            if ($current->id == $id) {
                break;
            }
            $current = $current->next;
        }
        return $current->name = $name;
    }
}
$lists = new singelLinkList ();
$lists->addLink ( new node ( 5, 'eeeeee' ) );
$lists->addLink ( new node ( 1, 'aaaaaa' ) );
$lists->addLink ( new node ( 6, 'ffffff' ) );
$lists->addLink ( new node ( 4, 'dddddd' ) );
$lists->addLink ( new node ( 3, 'cccccc' ) );
$lists->addLink ( new node ( 2, 'bbbbbb' ) );
$lists->getLinkList ();
echo "<br>-----------删除节点--------------<br>";
$lists->delLink ( 5 );
$lists->getLinkList ();
echo "<br>-----------更新节点名称--------------<br>";
$lists->updateLink ( 3, "222222" );
$lists->getLinkList ();
echo "<br>-----------获取节点名称--------------<br>";
echo $lists->getLinkNameById ( 5 );
echo "<br>-----------获取链表长度--------------<br>";
echo $lists->getLinkLength ();