Steque

1.对列是需要两个节点的，first和last。 last用于入列操作

2.pop和psuh操作需要的是first、

迭代器这里需要主要，操作的时候要从新new一个Node实例，不然的话就会导致原来的first被操作。

代码：

package chapter1.a3;

import edu.princeton.cs.algs4.StdOut;

import org.jetbrains.annotations.NotNull;

import java.util.Iterator;

/**

* Created by fengjw on 2017/8/14

* Code Change The World!

*/

public class Example1332<Item> implements Iterable<Item>{

private Node first;

private Node last;

public class Node{

Item item;

Node next;

}

public boolean isEmpty(){

return first == null;

}

public void enqueue(Item item){ // thr order

Node node = new Node();

node.item = item;

node.next = null;

if (isEmpty()){

first = node;

last = node;

}else {

last.next = node;

last = node;

}

}

public void push(Item e){

Node node = new Node();

node.item = e;

if (isEmpty()){

first = node;

last = node;

node.next = null;

}else {

node.next = first;

first = node;

}

}

public Item pop(){

if (isEmpty()){

return null;

}else {

Item item = first.item;

first = first.next;

return item;

}

}

@NotNull

@Override

public Iterator<Item> iterator() {

return new Iter();

}

private class Iter implements Iterator<Item>{

private Node current = first; //"current" function is not change the LinkedList first.

@Override

public boolean hasNext() {

return current != null;

}

@Override

public Item next() {

Item item = current.item;

current = current.next;

return item;

}

}

//test

public static void main(String [] args){

Example1332<String> steque = new Example1332<>();

steque.enqueue("a");

steque.enqueue("b");

steque.enqueue("c");

steque.enqueue("d");

steque.push("e");

steque.push("f");

steque.push("g");

//StdOut.println(steque);

StdOut.println("---------------");

Iterator<String> iterator = steque.iterator();

while (iterator.hasNext()){

StdOut.println(iterator.next());

}

StdOut.println("---------------");

StdOut.println("pop up: ");

while (!steque.isEmpty()){

StdOut.println(steque.pop());

}

}

}