双栈实现队列

双栈实现队列

class MyQueue {
    Deque<Integer> inStack;
    Deque<Integer> outStack;

    public MyQueue() {
        inStack = new LinkedList<Integer>();
        outStack = new LinkedList<Integer>();
    }
    
    public void push(int x) {
        inStack.push(x);
    }
    
    public int pop() {
        if (outStack.isEmpty()) {
            while (!inStack.isEmpty()) {
                outStack.push(inStack.pop());
            }
        }
        return outStack.pop();
    }
    
    public int peek() {
        if (outStack.isEmpty()) {
             while (!inStack.isEmpty()) {
                 //pop是返回并删除元素
                outStack.push(inStack.pop());
            }
        }
        return outStack.peek();
    }
    
    public boolean empty() {
        return inStack.isEmpty() && outStack.isEmpty();
    }
    
}