package javalearning;

import java.util.Stack;

public class TwoStacksQueue {
	public Stack<Integer> stackPush;//压入栈
	public Stack<Integer> stackPop;//弹出栈
	public TwoStacksQueue(){
		stackPush=new Stack<Integer>();
		stackPop=new Stack<Integer>();
	}
	/**
	 * 
	 * @param pushInt
	 * add:增加一个元素 如果队列已满，则抛出异常
	 */
    public void add(int pushInt){
    	stackPush.push(pushInt);
    }
    /**
     * 
     * poll:移除并返回队列头部的元素，如果队列为空，则返回null
     */
    public int poll(){
    	if(stackPop.empty()&&stackPush.empty()){
    		throw new RuntimeException("Queue is empty");
    	}else if(stackPop.empty()){
    		while(!stackPush.empty()){
    			stackPop.push(stackPush.pop());
    		}
    	}
    	return stackPop.pop();
    }
    /**
     * 
     * peek:返回队列头部的元素，如果队列为空，则阻塞
     */
    public int peek(){
    	if(stackPop.empty()&&stackPush.empty()){
    		throw new RuntimeException("Queue is empty");
    	}
    	else if(stackPop.empty()){
    		while(!stackPush.empty()){
    			stackPop.push(stackPush.pop());
    		}
    	}
    	return stackPop.peek();
    }
}