题解 | 用两个栈实现队列

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

public class Solution {
    Stack<Integer> stack1 = new Stack<Integer>();//入
    Stack<Integer> stack2 = new Stack<Integer>();//出

    public void push(int node) {
        stack1.push(node);
    }

    public int pop() {
        if (stack2.isEmpty()) {
            while (!stack1.isEmpty()) {
                stack2.push(stack1.pop());
            }
        }
        return stack2.pop();
    }
}