解法

class MyStack {
    // 主队列
    private Queue<Integer> queue1;
    // 辅助队列
    private Queue<Integer> queue2;

    /** Initialize your data structure here. */
    public MyStack() {
        queue1 = new LinkedList<>();
        queue2 = new LinkedList<>();
    }
    
    /** Push element x onto stack. */
    public void push(int x) {
        // 先放入辅助队列，再将队列1的放进到队列2，这样最后放入的就在最前面了
        queue2.offer(x);
        while (!queue1.isEmpty()) {
            queue2.offer(queue1.poll());
        }
        Queue<Integer> temp = queue2;
        queue2 = queue1;
        queue1 = temp;
    }
    
    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
        return queue1.poll();
    }
    
    /** Get the top element. */
    public int top() {
        return queue1.peek();
    }
    
    /** Returns whether the stack is empty. */
    public boolean empty() {
        return queue1.isEmpty();
    }
}

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * boolean param_4 = obj.empty();
 */