TwoStackQueue.java

package stack_and_queue;

import java.util.Stack;

/**
 * @Author: Wenhang Chen
 * @Description:由两个栈实现的队列
 * @Date: Created in 9:55 10/28/2019
 * @Modified by:
 */
public class TwoStackQueue {
 public Stack<Integer> stackPush;
 public Stack<Integer> stackPop;

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

 // push栈向pop栈倒入数据
 private void pushToPop() {
 if (stackPop.empty()) {
 while (!stackPush.empty()) {
 stackPop.push(stackPush.pop());
 }
 }
 }

 public void add(int pushInt) {
 stackPush.push(pushInt);
 }

 public int poll() {
 if (stackPush.empty() && stackPop.empty()) {
 throw new RuntimeException("Queue is empty!");
 }
 pushToPop();
 return stackPop.pop();
 }

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

 public static void main(String[] args) {
 TwoStackQueue twoStackQueue = new TwoStackQueue();
 twoStackQueue.add(1);
 twoStackQueue.add(2);
 System.out.println(twoStackQueue.poll());
 System.out.println(twoStackQueue.poll());
 twoStackQueue.add(3);
 System.out.println(twoStackQueue.poll());
 }
}