剑指offer牛客--用两个栈实现队列

要考虑到队列可能为空情况，抛异常。这样才全面。 

import java.util.Stack;public class Solution {Stack stack1 = new Stack();Stack stack2 = new Stack();public void push(int node) {stack1.push(node);}public int pop() throws Exception{if(!stack2.isEmpty())return stack2.pop();while(!stack1.isEmpty()){stack2.push(stack1.pop());}if(stack2.isEmpty())throw new RuntimeException("the queue is empty");return stack2.pop();}
}