算法笔试面试2

用两个栈来模拟实现队列

public class MyQueue {

    private static Stack<Integer> inStack;
    private static Stack<Integer> outStack;

    public MyQueue(){
        inStack = new Stack<>();
        outStack = new Stack<>();
    }

    // 像队列中push元素
    public void push(int x){
        inStack.push(x);
    }

    // 从队列中弹出元素
    public int pop(){
        if (outStack.isEmpty()){
            in2out();
        }
        return outStack.pop();
    }

    // 查看队首元素，但是不取出
    public int peek(){
        if(outStack.isEmpty()){
            in2out();
        }
        return outStack.peek();
    }

    public boolean isEmpty(){
        return inStack.isEmpty() && outStack.isEmpty();
    }

    public void in2out(){
        while (!inStack.isEmpty()){
            outStack.push(inStack.pop());
        }
    }

}