package basic.stackqueue;

import java.util.Stack;

/**
 * 使用栈结构实现队列结构的功能
 *
 * 微信公众号:Java和算法学习
 *
 * @author 周一
 */
public class TwoStacksImplementQueue {

 /**
 * 使用两个栈来实现队列结构
 */
 public static class TwoStackQueue<T> {
 // 用于存放添加数据的栈
 public Stack<T> stackPush;
 // 用于存放获取数据的栈
 public Stack<T> stackPop;

 public TwoStackQueue() {
 stackPush = new Stack<>();
 stackPop = new Stack<>();
 }

 /**
 * 倒数据
 */
 private void pushToPop() {
 // pop为空才倒数据
 if (stackPop.empty()) {
 // push有数据可倒,并且一次性倒完
 while (!stackPush.empty()) {
 stackPop.push(stackPush.pop());
 }
 }
 }

 /**
 * 添加数据都往stackPush栈放
 */
 public void add(T data) {
 stackPush.push(data);
 }

 public T poll() {
 if (stackPush.empty() && stackPop.empty()) {
 throw new RuntimeException("Queue is empty");
 }
 // 拿数据前先执行倒数据方法
 pushToPop();
 // 拿数据都从stackPop栈拿
 return stackPop.pop();
 }

 public T peek() {
 if (stackPush.empty() && stackPop.empty()) {
 throw new RuntimeException("Queue is empty");
 }
 pushToPop();
 return stackPop.peek();
 }

 }

 public static void main(String[] args) {
 TwoStackQueue<Integer> test = new TwoStackQueue<>();
 test.add(1);
 test.add(4);
 test.add(3);
 test.add(2);

 System.out.println(test.peek());
 System.out.println(test.poll());

 System.out.println(test.peek());
 System.out.println(test.poll());

 System.out.println(test.peek());
 System.out.println(test.poll());

 System.out.println(test.peek());
 System.out.println(test.poll());
 }

}