/*

* @lc app=leetcode id=232 lang=java

*

* [232] Implement Queue using Stacks

push(x) -- 将一个元素放入队列的尾部。

pop() -- 从队列首部移除元素，不返回

top() -- 仅限c++，java内没有

peek() -- 返回队列首部的元素。

empty() -- 返回队列是否为空。

*/

// @lc code=start

class MyQueue {

Stack<Integer> stackIn; //声明变量，没有实际的对象（declaration of a variable)

Stack<Integer> stackOut;

//initialize the data structurea here, stackIn and stackOut

public MyQueue() {

stackIn = new Stack<>(); //allocates an object and make stackIn reference that object

stackOut = new Stack<>();

}

//push element x to the back of queue;

public void push(int x) {

stackIn.push(x);

}

//remove the element from the front of queue and return that element.

public int pop() {

// check while stackOut is empty, move all elements from stackIn to stackOut

if(stackOut.empty()) {

while(!stackIn.empty()) {

stackOut.push(stackIn.pop());

}

}

return stackOut.pop();

}

//Get the front element(只查询数值，不弹出，所以还需要借助push来放回去)

public int peek() {

int res=this.pop(); //这里直接调用同一个类下面的pop函数（This directly calls the pop function from the same class.）

stackOut.push(res);

return res;

}

public boolean empty() {

return stackIn.empty() && stackOut.empty();

}

}

/**

* Your MyQueue object will be instantiated and called as such:

* MyQueue obj = new MyQueue();

* obj.push(x);

* int param_2 = obj.pop();

* int param_3 = obj.peek();

* boolean param_4 = obj.empty();

*/

// @lc code=end