数据结构和算法-009 双向链表
双向链表，就是在一个节点（node）有两个指针（point），分别指向前一个节点和后一个节点，它和链表最大的区别就是，链表是单向的，只能找到后面的节点，不能往前找，双向链表顾名思义，双向的，可以往后找，也可以往前。
这段代码有点复杂，先看看，再一点点解释吧
public class DoubleLinkList {
Neighbor firstLink;
Neighbor lastLink;
public void insertFirstPosition(String ownerName, int houseNumber){
Neighbor newLink = new Neighbor(ownerName, houseNumber);
if(isEmpty()){
lastLink = newLink;
} else {
firstLink.previous= newLink;
}
newLink.next= firstLink;
firstLink = newLink;
}
public void insertLastPosition(String ownerName, int houseNumber){
Neighbor newLink = new Neighbor(ownerName, houseNumber);
if(isEmpty()){
firstLink = newLink;
} else {
lastLink.next= newLink;
newLink.previous= lastLink;
}
lastLink = newLink;
}
public void insertInOrder(String ownerName, int houseNumber){
Neighbor newLink = new Neighbor(ownerName, houseNumber);
Neighbor previousLink= null;
Neighbor currentLink = firstLink;
while (currentLink!= null && houseNumber>currentLink.houseNumber){
previousLink =currentLink;
currentLink = currentLink.next;
}
if(previousLink == null){
firstLink = newLink;
}else{
previousLink.next= newLink;
}
newLink.next = currentLink;
}
public boolean insertAfterKey(String ownerName, int houseNumber, int key){
Neighbor newLink = new Neighbor(ownerName, houseNumber);
Neighbor currentLink = firstLink;
while (currentLink.houseNumber != key){
currentLink = currentLink.next;
if(currentLink== null){
return false;
}
}
if(currentLink == lastLink){
newLink.next= null;
lastLink = newLink;
}else{
newLink.next= currentLink.next;
currentLink.next.previous = newLink;
}
newLink.previous=currentLink;
currentLink.next= newLink;
return true;
}
public boolean isEmpty(){
return firstLink == null && lastLink == null;
}
public void display(){
Neighbor theLink =firstLink;
while (theLink != null){
theLink.printNerghbor();
System.out.println("Next Link: " + theLink.next);
theLink= theLink.next;
}
}
public static void main(String[] args) {
System.out.println("Create a DoubleLinkList");
DoubleLinkList linkedList = new DoubleLinkList();
System.out.println();
System.out.println("Add First Node at fitst position");
linkedList.insertFirstPosition("Lucio", 7);
linkedList.display();
System.out.println();
System.out.println("Add Second Node at fitst position");
linkedList.insertFirstPosition("Matt", 6);
linkedList.display();
System.out.println();
System.out.println("Add Third Node at last position");
linkedList.insertLastPosition("Leo", 500);
linkedList.display();
System.out.println();
System.out.println("Add Fouth Node at last position");
linkedList.insertLastPosition("Angela", 501);
linkedList.display();
System.out.println();
System.out.println("Add a Node in order house number");
linkedList.insertInOrder("Jack", 143);
linkedList.display();
System.out.println();
System.out.println("Add another two Nodes in order house number");
linkedList.insertInOrder("James", 122);
linkedList.insertInOrder("Renee", 155);
linkedList.display();
System.out.println();
System.out.println("Add a Nodes after special house number");
linkedList.insertAfterKey("Jason", 123, 143);
linkedList.display();
System.out.println();
System.out.println("Create Iterator for DoubleLinkList");
NeighborIterator neighbors = new NeighborIterator(linkedList);
System.out.println();
System.out.println("Print current Node in the Linklist");
neighbors.currentLink.printNerghbor();
System.out.println();
System.out.println("Current Node has next None: " + neighbors.hasNext());
System.out.println();
System.out.println("Go to next 2 node");
neighbors.next();
neighbors.next();
System.out.println();
System.out.println("Print current Node in the Linklist");
neighbors.currentLink.printNerghbor();
System.out.println();
System.out.println("Print next node");
neighbors.next().printNerghbor();
System.out.println();
System.out.println("Print current Node in the Linklist");
neighbors.currentLink.printNerghbor();
System.out.println();
System.out.println("Remove Current Node");
neighbors.remove();
System.out.println();
linkedList.display();
}
}
class NeighborIterator{
Neighbor currentLink;
Neighbor previousLink;
DoubleLinkList linkList;
NeighborIterator(DoubleLinkList linkList){
this.linkList = linkList;
currentLink = linkList.firstLink;
previousLink = linkList.lastLink;
}
public boolean hasNext(){
if(currentLink.next != null){
return true;
}
return false;
}
public Neighbor next(){
if(hasNext()){
previousLink= currentLink;
currentLink = currentLink.next;
return currentLink;
}
return null;
}
public void remove(){
if(previousLink == null){
linkList.firstLink= currentLink.next;
} else {
previousLink.next = currentLink.next;
if(currentLink.next == null){
currentLink =linkList.firstLink;
previousLink = null;
} else {
currentLink = currentLink.next;
currentLink.previous=previousLink;
}
}
}
}
class Neighbor{
public String ownerName;
public int houseNumber;
public Neighbor next;
public Neighbor previous;
Neighbor(String ownerName, int houseNumber){
this.ownerName = ownerName;
this.houseNumber = houseNumber;
}
public void printNerghbor(){
System.out.println(ownerName + ": " + houseNumber);
}
public String toString(){
return this.ownerName;
}
}
Neighbor 就是节点（Node），可以看到两个引用，一个指向前一个节点（previous），一个指向后一个(next)。
public Neighbor next; public Neighbor previous;
其他的自己看了
DoubleLinkList 就是双向链表
两个引用指向起始和结尾的节点，
Neighbor firstLink; Neighbor lastLink;
解释以下头部插入的方法
public void insertFirstPosition(String ownerName, int houseNumber){
// 创建一个节点
Neighbor newLink = new Neighbor(ownerName, houseNumber);
// 如过链表为空
if(isEmpty()){
// 把新节点设为最后一个节点
lastLink = newLink;
} else {//链表不为空
// 把新节点设为第一个节点之前的节点
firstLink.previous= newLink;
}
// 新节点的后的节点设为当前第一个节点
newLink.next= firstLink;
// 把新节点设为第一个节点
firstLink = newLink;
}
不知道看懂没有，简单说就是把新节点放在最前面，然后调整引用，在第一个节点设为新节点。
后面一个方法不解释了，意思差不多。
NeihbourIterator 是一个简单的Iterator，实现了hasNext() 和next()方法
通过两个引用实现控制
Neighbor currentLink; Neighbor previousLink;
remove（删除）的方法写NeighborIterator类中是因为DoubleLinkedList类过于简单，无法获得当前节点。正好Iterator可以获得。在Java.util中的LindedList带有remove方法，但是是和索引一起使用的。
输出结果
Create a DoubleLinkList Add First Node at fitst position Lucio: 7 Next Link: null Add Second Node at fitst position Matt: 6 Next Link: Lucio Lucio: 7 Next Link: null Add Third Node at last position Matt: 6 Next Link: Lucio Lucio: 7 Next Link: Leo Leo: 500 Next Link: null Add Fouth Node at last position Matt: 6 Next Link: Lucio Lucio: 7 Next Link: Leo Leo: 500 Next Link: Angela Angela: 501 Next Link: null Add a Node in order house number Matt: 6 Next Link: Lucio Lucio: 7 Next Link: Jack Jack: 143 Next Link: Leo Leo: 500 Next Link: Angela Angela: 501 Next Link: null Add another two Nodes in order house number Matt: 6 Next Link: Lucio Lucio: 7 Next Link: James James: 122 Next Link: Jack Jack: 143 Next Link: Renee Renee: 155 Next Link: Leo Leo: 500 Next Link: Angela Angela: 501 Next Link: null Add a Nodes after special house number Matt: 6 Next Link: Lucio Lucio: 7 Next Link: James James: 122 Next Link: Jack Jack: 143 Next Link: Jason Jason: 123 Next Link: Renee Renee: 155 Next Link: Leo Leo: 500 Next Link: Angela Angela: 501 Next Link: null Create Iterator for DoubleLinkList Print current Node in the Linklist Matt: 6 Current Node has next None: true Go to next 2 node Print current Node in the Linklist James: 122 Print next node Jack: 143 Print current Node in the Linklist Jack: 143 Remove Current Node Matt: 6 Next Link: Lucio Lucio: 7 Next Link: James James: 122 Next Link: Jason Jason: 123 Next Link: Renee Renee: 155 Next Link: Leo Leo: 500 Next Link: Angela Angela: 501 Next Link: null