Doubly linked list is a very important data structure for PHP development programs. You can think of a PHP array as a doubly linked list, and PHP's built-in SplDoublyLinkedList class implements iterators, array access and interfaces for obtaining quantities. Make program access to objects as convenient as accessing arrays.
SplDoublyLinkedList class code is as follows:
<?php
/**
* PS：关于预定义接口Iterator, ArrayAccess, Countable的文章已经介绍过了，不认识的可以往前翻翻
*/
class SplDoublyLinkedList implements Iterator, ArrayAccess, Countable
{
/**
* @var _llist 定义一个数组用于存放数据
*/
protected $_llist = array();
/**
* @var _it_mode 链表的迭代模式
*/
protected $_it_mode = 0;
/**
* @var _it_pos 链表指针
*/
protected $_it_pos = 0;
/**
* 迭代模式
* @see setIteratorMode
*/
const IT_MODE_LIFO = 0x00000002;
const IT_MODE_FIFO = 0x00000000;
const IT_MODE_KEEP = 0x00000000;
const IT_MODE_DELETE = 0x00000001;
/**
* @return 返回被移出尾部节点元素
* @throw RuntimeException 如果链表为空则抛出异常
*/
public function pop()
{
if (count($this->_llist) == 0) {
throw new RuntimeException("Can't pop from an empty datastructure");
}
return array_pop($this->_llist);
}
/**
* @return 返回被移出头部节点元素
* @throw RuntimeException 如果链表为空则抛出异常
*/
public function shift()
{
if (count($this->_llist) == 0) {
throw new RuntimeException("Can't shift from an empty datastructure");
}
return array_shift($this->_llist);
}
/**
* 往链表尾部添加一个节点元素
* @param $data 要添加的节点元素
*/
public function push($data)
{
array_push($this->_llist, $data);
return true;
}
/**
* 往链表头部添加一个节点元素
* @param $data 要添加的节点元素
*/
public function unshift($data)
{
array_unshift($this->_llist, $data);
return true;
}
/**
* @return 返回尾部节点元素，并把指针指向尾部节点元素
*/
public function top()
{
return end($this->_llist);
}
/**
* @return 返回头部节点元素，并把指针指向头部节点元素
*/
public function bottom()
{
return reset($this->_llist);
}
/**
* @return 返回链表节点数
*/
public function count()
{
return count($this->_llist);
}
/**
* @return 判断链表是否为空
*/
public function isEmpty()
{
return ($this->count() == 0);
}
/**
* 设置迭代模式
* - 迭代的顺序 (先进先出、后进先出)
* - SplDoublyLnkedList::IT_MODE_LIFO (堆栈)
* - SplDoublyLnkedList::IT_MODE_FIFO (队列)
*
* - 迭代过程中迭代器的行为
* - SplDoublyLnkedList::IT_MODE_DELETE (删除已迭代的节点元素)
* - SplDoublyLnkedList::IT_MODE_KEEP (保留已迭代的节点元素)
*
* 默认的模式是 0 : SplDoublyLnkedList::IT_MODE_FIFO | SplDoublyLnkedList::IT_MODE_KEEP
*
* @param $mode 新的迭代模式
*/
public function setIteratorMode($mode)
{
$this->_it_mode = $mode;
}
/**
* @return 返回当前的迭代模式
* @see setIteratorMode
*/
public function getIteratorMode()
{
return $this->_it_mode;
}
/**
* 重置节点指针
*/
public function rewind()
{
if ($this->_it_mode & self::IT_MODE_LIFO) {
$this->_it_pos = count($this->_llist)-1;
} else {
$this->_it_pos = 0;
}
}
/**
* @return 判断指针对应的节点元素是否存在
*/
public function valid()
{
return array_key_exists($this->_it_pos, $this->_llist);
}
/**
* @return 返回当前指针的偏移位置
*/
public function key()
{
return $this->_it_pos;
}
/**
* @return 返回当前指针对应的节点元素
*/
public function current()
{
return $this->_llist[$this->_it_pos];
}
/**
* 将指针向前移动一个偏移位置
*/
public function next()
{
if ($this->_it_mode & self::IT_MODE_LIFO) {
if ($this->_it_mode & self::IT_MODE_DELETE) {
$this->pop();
}
$this->_it_pos--;
} else {
if ($this->_it_mode & self::IT_MODE_DELETE) {
$this->shift();
} else {
$this->_it_pos++;
}
}
}
/**
* @return 偏移位置是否存在
*
* @param $offset 偏移位置
* @throw OutOfRangeException 如果偏移位置超出范围或者无效则抛出异常
*/
public function offsetExists($offset)
{
if (!is_numeric($offset)) {
throw new OutOfRangeException("Offset invalid or out of range");
} else {
return array_key_exists($offset, $this->_llist);
}
}
/**
* @return 获取偏移位置对应的值
*
* @param $offset 偏移位置
* @throw OutOfRangeException 如果偏移位置超出范围或者无效则抛出异常
*/
public function offsetGet($offset)
{
if ($this->_it_mode & self::IT_MODE_LIFO) {
$realOffset = count($this->_llist)-$offset;
} else {
$realOffset = $offset;
}
if (!is_numeric($offset) || !array_key_exists($realOffset, $this->_llist)) {
throw new OutOfRangeException("Offset invalid or out of range");
} else {
return $this->_llist[$realOffset];
}
}
/**
* @return 设置偏移位置对应的值
*
* @param $offset 偏移位置
* @throw OutOfRangeException 如果偏移位置超出范围或者无效则抛出异常
*/
public function offsetSet($offset, $value)
{
if ($offset === null) {
return $this->push($value);
}
if ($this->_it_mode & self::IT_MODE_LIFO) {
$realOffset = count($this->_llist)-$offset;
} else {
$realOffset = $offset;
}
if (!is_numeric($offset) || !array_key_exists($realOffset, $this->_llist)) {
throw new OutOfRangeException("Offset invalid or out of range");
} else {
$this->_llist[$realOffset] = $value;
}
}
/**
* @return 删除偏移位置对应的值
*
* @param $offset 偏移位置
* @throw OutOfRangeException 如果偏移位置超出范围或者无效则抛出异常
*/
public function offsetUnset($offset)
{
if ($this->_it_mode & self::IT_MODE_LIFO) {
$realOffset = count($this->_llist)-$offset;
} else {
$realOffset = $offset;
}
if (!is_numeric($offset) || !array_key_exists($realOffset, $this->_llist)) {
throw new OutOfRangeException("Offset invalid or out of range");
} else {
array_splice($this->_llist, $realOffset, 1);
}
}
}
?>Example description:
<?php
$doubly=new SplDoublyLinkedList();
$doubly->push('a');
$doubly->push('b');
$doubly->push('c');
$doubly->push('d');
echo '初始链表结构：';
var_dump($doubly);
echo '<br/> 先进先出Keep模式迭代输出： <br/>';
$doubly->setIteratorMode(SplDoublyLinkedList::IT_MODE_FIFO | SplDoublyLinkedList::IT_MODE_KEEP);
$doubly->rewind();
foreach($doubly as $key=>$value)
{
echo $key.' '.$value."<br/>";
}
echo '<br/>后进先出Keep模式迭代输出：<br/>';
$doubly->setIteratorMode(SplDoublyLinkedList::IT_MODE_LIFO | SplDoublyLinkedList::IT_MODE_KEEP);
$doubly->rewind();
foreach($doubly as $key=>$value)
{
echo $key.' '.$value."<br/>";
}
echo '<br/>后进先出Delete模式迭代输出：<br/>';
$doubly->setIteratorMode(SplDoublyLinkedList::IT_MODE_LIFO | SplDoublyLinkedList::IT_MODE_DELETE);
$doubly->rewind();
foreach($doubly as $key=>$value)
{
if($key == 1) break;
echo $key.' '.$value."<br/>";
}
echo '<br/>Delete模式迭代之后的链表：';
var_dump($doubly);
?>
Output:
Initial linked list structure:
object(SplDoublyLinkedList)[1] private 'flags' => 0
private 'dllist' =>
array (size=4)
0 => 'a' (length=1)
1 => 'b' (length=1)
2 => 'c' (length=1)
3 => 'd' (length=1)
FIFO Keep mode iteration output:
0 a
1 b
2 c
3 d
LIFO Keep mode iteration output:
3 d
2 c
1 b
0 a
LIFO Delete mode iteration output:
3 d
2 c
Linked list after Delete mode iteration:
object(SplDoublyLinkedList)[1] private 'flags' => 3
private 'dllist' =>
array (size=2)
0 => 'a' (length=1)
1 => 'b' (length=1)The last question: SplDoublyLinkedList::IT_MODE_FIFO | SplDoublyLinkedList: :What is the output of iteration in IT_MODE_KEEP mode?
Related recommendations:
Detailed explanation of the basics of PHP doubly linked list
Definition and use of JavaScript doubly linked list
PHP implements an example code of a doubly linked list
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