php 栈的实现

php class Stack { private $stack; public function __construct() { $this->stack = array(); } public function push($item) { array_push($this->stack, $item); } public function pop() { if (!$this->isEmpty()) { return array_pop($this->stack); } return null; } public function isEmpty() { return empty($this->stack); } public function top() { return end($this->stack); } }