牛客-TOP101-BM42

import java.util.*;
import java.util.Stack;

public class Solution {
    
    Stack<Integer> stack1 = new Stack<Integer>();
    Stack<Integer> stack2 = new Stack<Integer>();
    
    public void push(int node) {
    
        stack1.push(node);
    }
    
    public int pop() {
    
        while(!stack1.isEmpty()){
    
            stack2.push(stack1.pop());
        }
        int num = stack2.pop();
        while(!stack2.isEmpty()){
    
            stack1.push(stack2.pop());
        }
        return num;
    }
}