模拟题 02 用栈实现队列

• 思路
  • 两个栈，入队一直用第一个栈，出队，把第一个栈数据倒转到第二栈，第二个栈的基本操作，就跟队列基本操作一致。
• 代码

public  class MyQueue {
    public static void main(String[] args) {
        MyQueue myQueue = new MyQueue();
        myQueue.push(1);
        myQueue.push(2);
        myQueue.push(3);
        myQueue.push(4);
        myQueue.push(5);
        while (!myQueue.empty()) {
            System.out.println(myQueue.pop());
        }
    }
        Stack<Integer> stackIn= new Stack<>();;
        Stack<Integer>stackIn2 =new Stack<>();
        /** Initialize your data structure here. */
        public MyQueue() {
        }

        /** Push element x to the back of queue. */
        public void push(int x) {
            if(stackIn.isEmpty()) {
                while (!stackIn2.isEmpty()) {
                    stackIn.push(stackIn2.pop());
                }
            }
            stackIn.push(x);
        }

        /** Removes the element from in front of queue and returns that element. */
        public int pop() {

            if(stackIn2.isEmpty()) {
                while (!stackIn.isEmpty()) {
                    stackIn2.push(stackIn.pop());
                }
            }
            return stackIn2.pop();
        }

        /** Get the front element. 改进 */
        public int peek() {
            if(stackIn2.isEmpty()) {
                while (!stackIn.isEmpty()) {
                    stackIn2.push(stackIn.pop());
                }
            }
            return stackIn2.peek();
        }

        /** Returns whether the queue is empty. */
        public boolean empty() {
            if(stackIn.isEmpty() && stackIn2.isEmpty()) {
                return true;
            }
            return false;
        }
}