学习队列，用栈实现队列。题源：https://leetcode-cn.com/probl...思路：准备两个栈inStack和outStack入队时，出队时push到inStack，(1)：若outStack为空,将inStack中的所有元素一一弹出,push到outStack,outStack弹出栈顶元素(2):如果outStack不为空,outStack弹出栈顶元素php实现代码inStack=newStack();$this->outStack=newStack();}/***@param$item*压入一个元素*入队*/publicfunctionpush($item){$this->inStack->push($item);}/***弹出一个元素*出队*/publicfunctionpop(){$this->checkOutStack();返回$this->outStack->pop();}/***获取队列的头元素*/publicfunctionpeek(){$this->checkOutStack();返回$this->outStack->top();}/***返回队列是否为空。*@returnBoolean*/publicfunctionempty(){return$this->inStack->isEmpty()&&$this->outStack->isEmpty();}}privatefunctioncheckOutStack(){if($this->outStack->isEmpty()){//如果出栈（outStack）栈为空，弹出所有入队（inStack）栈元素，放入出栈栈outStackwhile(!$this->inStack->isEmpty()){$this->outStack->push($this->inStack->pop());}}}}}源码下载：gitee
