stack_queue.php

<?php
/**
 * 通过两个栈实现队列
 * Author: 学院君
 */

class StackQueue
{
 /**
 * 用于push数据
 * @var SplStack
 */
 protected $stack1;
 /**
 * 用于pop数据
 * @var SplStack
 */
 protected $stack2;

 public function __construct()
 {
 $this->stack1 = new SplStack();
 $this->stack2 = new SplStack();
 }

 /**
 * 往队列中添加队尾元素
 * @param $value
 */
 public function pushToTail($value)
 {
 $this->stack1->push($value);
 }

 /**
 * 从队列中删除队头元素
 * @return mixed
 * @throws Exception
 */
 public function popFromHead()
 {
 if ($this->stack2->isEmpty()) {
 if (!$this->stack1->isEmpty()) {
 $value = $this->stack1->pop();
 $this->stack2->push($value);
 }
 }
 if ($this->stack2->isEmpty()) {
 throw new Exception('Queue is empty.');
 }

 return $this->stack2->pop();
 }
}

//测试代码
$queue = new StackQueue();
$queue->pushToTail(100);
$queue->pushToTail('PHP面试题');
$queue->pushToTail('学院君');
try {
 while ($value = $queue->popFromHead()) {
 var_dump($value);
 }
} catch (Exception $exception) {
 echo $exception->getMessage();
}
echo "\n";
exit();