# 算法练习(39): 以栈为目标的队列Steque(1.3.32)

• 链表节点增删查改
• 环形链表

### 题目

1.3.32 Steque。一个以栈为目标的队列（或称steque），是一种支持push、pop和enqueue操作的数据类型。为这种抽象数据类型定义一份API并给出一份基于链表的实现。

1.3.32 Steque. A stack-ended queue or steque is a data type that supports push, pop, and enqueue. Articulate an API for this ADT. Develop a linked-list-based implementation.

### 答案

``````public class Steque<Item> implements Iterable<Item>{

private class Node {
Node next;
Item item;
}

private Node first;
private Node last;

public void push(Item x){
Node node = new Node();
node.item = x;
if (this.isEmpty()) {
first = node;
last = node;
}else{
node.next = first;
first = node;
}
}

public Item pop(){
if (this.isEmpty()) {
return null;
}
Item item = first.item;
first = first.next;
return item;
}

public void enqueue(Item x){
Node node = new Node();
node.item = x;
if (this.isEmpty()) {
first = node;
last = node;
}else{
last.next = node;
last = node;
}
}

public boolean isEmpty(){
return first == null;
}

public Iterator<Item> iterator()
{
return new StequeIterator();
}

private class StequeIterator implements Iterator<Item>
{
private Node current = first;

public boolean hasNext()
{
return current != null;
}

public Item next()
{
Item x = current.item;
current = current.next;
return x;
}
}

public static void main(String[] args) {
// TODO Auto-generated method stub
Steque<String> stringSteque1 = new Steque<String>();
stringSteque1.enqueue("我");
stringSteque1.enqueue("的");
stringSteque1.enqueue("名字");
stringSteque1.enqueue("叫顶级程序员不穿女装");
stringSteque1.enqueue("微博:https://m.weibo.cn/p/1005056186766482");

for (String string : stringSteque1) {
System.out.println(string);
}

Steque<String> stringSteque2 = new Steque<String>();
stringSteque2.push("我");
stringSteque2.push("的");
stringSteque2.push("名字");
stringSteque2.push("叫顶级程序员不穿女装");
stringSteque2.push("微博:https://m.weibo.cn/p/1005056186766482");

for (String string : stringSteque2) {
System.out.println(string);
}

}

}
``````

Steque.java