Java双栈

class MyQueue {

Stack<Integer>stack1;
Stack<Integer>stack2;
    /** Initialize your data structure here. */
    public MyQueue() {
         stack1=new Stack<>();
         stack2=new Stack<>();
    }

    /** Push element x to the back of queue. */
    public void push(int x) {
         stack1.push(x);
    }

    /** Removes the element from in front of queue and returns that element. */
    public int pop() {
         if(stack2.isEmpty()){
              if(stack1.isEmpty()) return -1;
              while(!stack1.isEmpty()) stack2.push(stack1.pop());
         }
         return stack2.pop();
    }

    /** Get the front element. */
    public int peek() {
        if(stack2.isEmpty()){
            if(stack1.isEmpty()) return -1;
            while(!stack1.isEmpty()) stack2.push(stack1.pop());
        }
        return stack2.peek();
    }

    /** Returns whether the queue is empty. */
    public boolean empty() {
         return stack1.isEmpty()&&stack2.isEmpty();
    }
}