PHP Class&Object -- PHP 实现链表

     链表是更复杂数据结构的基础，它的特性在于新元素可以添加到列表的任何位置，也可以从列表的任何位置删除元素，没有预先设置的尺寸限制，元素之间的相互次序也很容易管理。

    这些特性使链表与数组有了明显的区别。数组适合模仿数据处于特定位置的情况，但对于注重数据相对次序的信息来说，链表是较优的选择。

   // 来自 PHP5 in Practice  (U.S.)Elliott III & Jonathan D.Eisenhamer

    

下面我们使用对象来实现链表：

<?php // Define a class to implement linked lists, a linked list node. class Linked_List_Node { // Define the variable to hold our data: public $data; // And a variable to hold the next object in the chain: public $next; // A constructor method that allows for data to be passed in public function __construct($d = NULL) { $this->data = $d; } // Now create some methods that will make handling lists more automatic: // First of all a method that will insert a Node after this one public function insertAfter(Linked_List_Node $insert) { // This assumes a single node will be passed in not an entire list. // If you pass a node from a list the rest of the list will be lost. // Set the new node's next, to be this node's next. $insert->next = $this->next; // Now set this node's next, to the new node: $this->next = $insert; } // Now a method that will remove the node after this one: public function removeAfter() { // Store a reference to the node in question: $ref = $this->next; // Now jump over this node, linking to its child (if it existed) if (isset($this->next->next)) { $this->next = $this->next->next; } else { // Otherwise just make it null $this->next = NULL; } // Now, destroy the original object: unset($ref); } // Now also define a method that will output an entire linked // list, starting from this node. public function asString() { // If another child exists, then retrieve its value: $children = ''; if ($this->next) { $children = ', ' . $this->next->asString(); } // Return this data, concatenated with that of all it's children: return $this->data . $children; } } // Create a new linked list: $list = new Linked_List_Node('PHP'); // Now add an element after that one: $list->insertAfter(new Linked_List_Node('Perl')); // And then insert one in between the two: $list->insertAfter(new Linked_List_Node('Javascript')); // Echo this out as a string: PHP, Javascript, Perl echo '<p>', $list->asString(), '</p>'; // Now remove the last element: $list->next->removeAfter(); // And output the string again: PHP, Javascript echo '<p>', $list->asString(), '</p>'; ?>