题目描述

一个栈负责入队，一个栈负责出队列，差不多就如代码所示，具体可以画一个图就差不多了

样例

class MyQueue {
    Stack<Integer> inStack;
    Stack<Integer> outStack;
    /** Initialize your data structure here. */
    public MyQueue() {
        inStack = new Stack<>();
        outStack = new Stack<>();
    }

    /** Push element x to the back of queue. */
    public void push(int x) {
        inStack.push(x);
    }

    /** Removes the element from in front of queue and returns that element. */
    public int pop() {
        if(outStack.isEmpty()){
           while(!inStack.isEmpty()){
               outStack.push(inStack.pop());
           } 
        }
        return outStack.pop();
    }

    /** Get the front element. */
    public int peek() {
        if(outStack.isEmpty()){
           while(!inStack.isEmpty()){
               outStack.push(inStack.pop());
           } 
        }
        return outStack.peek();
    }

    /** Returns whether the queue is empty. */
    public boolean empty() {
        return outStack.isEmpty() && inStack.isEmpty();
    }
}