这里不是通过SPL队列(SplQueue)实现的,是一种思想的学习,先看什么是队列。
deque,全名double-ended queue,是一种具有队列和栈的性质的数据结构。双端队列中的元素可以从两端弹出,其限定插入和删除操作在表的两端进行。双向队列(双端队列)就像是一 个队列,但是你可以在任何一端添加或移除元素。而双端队列是一种数据结构,定义如下:
A deque is a data structure consisting of a list of items, on which the following operations are possible.
- push(D,X) -- insert item X on the rear end of deque D.
- pop(D) -- remove the front item from the deque D and return it.
- inject(D,X) -- insert item X on the front end of deque D.
- eject(D) -- remove the rear item from the deque D and return it.
Write routines to support the deque that take O(1) time per operation.
翻译:双端队列(deque)是由一些项的表组成的数据结构,对该数据结构可以进行下列操作:
- push(D,X) 将项X 插入到双端队列D的前端
- pop(D) 从双端队列D中删除前端项并将其返回
- inject(D,X) 将项X插入到双端队列D的尾端
- eject(D) 从双端队列D中删除尾端项并将其返回
编写支持双端队伍的例程,每种操作均花费O(1)时间
<?php
class deque
{
public $queue = array();
public $length = 0;
public function frontAdd($node){
array_unshift($this->queue,$node);
$this->countqueue();
}
public function frontRemove(){
$node = array_shift($this->queue);
$this->countqueue();
return $node;
}
public function rearAdd($node){
array_push($this->queue,$node);
$this->countqueue();
}
public function rearRemove(){
$node = array_pop($this->queue);
$this->countqueue();
return $node;
}
public function countqueue(){
$this->length = count($this->queue);
}
}
$fruit = new deque();
echo $fruit -> length;
$fruit -> frontAdd("Apple");
$fruit -> rearAdd("Watermelon");
echo '<pre>';
print_r($fruit);
echo '</pre>';
?>
程序运行结果:
0
deque Object
(
[queue] => Array
(
[0] => Apple
[1] => Watermelon
)
[length] => 2
)