用两个栈实现队列

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() {
//将第一个栈中内容弹出放入第二个栈中
while(!stack1.isEmpty())
stack2.push(stack1.pop());
//第二个栈栈顶就是最先进来的元素，即队首
int res = stack2.pop();
//再将第二个栈的元素放回第一个栈
while(!stack2.isEmpty())
stack1.push(stack2.pop());
return res;
}
}

 

参考：https://www.nowcoder.com/practice/54275ddae22f475981afa2244dd448c6?tpId=295&tqId=23281&ru=/exam/oj&qru=/ta/format-top101/question-ranking&sourceUrl=%2Fexam%2Foj