引言
在之前的博文中，我简单的向大家分享了一些链表相关的知识及一些面试题，如果感兴趣的老铁可以去瞧瞧！今天给大家带来双向链表以及带傀儡节点的双向链表的实现。认真看，每一步都有具体的来由和理解，希望对大家有所帮助！
详细步骤解析咋们边看代码边学习！
双向链表的实现
class ListNode{
public int val;//数值域
public ListNode prev;
public ListNode next;
public ListNode(int val) {
this.val = val;
}
}
public class DoubleLinkedList {
public ListNode head;//指向双链表的头节点
public ListNode last;//指向双链表尾巴节点
//打印链表--和打印单链表的方式一样
public void display(){
ListNode cur = this.head;
while (cur!=null) {
System.out.print(cur.val + " ");
cur = cur.next;
}
System.out.println();
}
//得到单链表的长度
public int size(){
int count = 0;//记录节点个数
ListNode cur = this.head;
while (cur!=null) {
count++;
cur = cur.next;
}
return count;
}
//查找是否包含关键字key是否在单链表当中
public boolean contains(int key){
ListNode cur = this.head;
while (cur!=null) {
if(cur.val == key) {//如果cur.val等于key返回真
return true;
}//否则继续往下走
cur = cur.next;
}
return false;
}
//头插法
public void addFirst(int data){
ListNode node = new ListNode(data);//new了个插入节点
if(head == null) {//如果插入时链表为空则，头和尾都指向新节点node
this.head = node;
this.last = node;
}else {
node.next = head;
head.prev = node;
this.head = node;
}
}
//尾插法
public void addLast(int data){
ListNode node = new ListNode(data);
if(this.head == null) {
this.head = node;
this.last = node;
}else {
this.last.next = node;
node.prev = last;
this.last = node;
}
}
//任意位置插入,第一个数据节点为0号下标
public void addIndex(int index,int data){
ListNode node = new ListNode(data);
if(index<0 || index>size()){
System.out.println("index位置不合法");
}
if(index == 0) {
addFirst(data);
}
if(index==size()){
addLast(data);
}
ListNode cur = searchIndex(index);
node.next = cur.prev.next;
cur.prev.next = node;
node.prev = cur.prev;
cur.prev = node;
}
public ListNode searchIndex(int index) {
ListNode cur = this.head;//创建个方法找到插入时cur的位置
while (index != 0) {
cur = cur.next;
index--;
}
return cur;
}
//删除第一次出现关键字为key的节点
//单链表中删除第一次出现的关键字需要找到关键字前驱
//双链表只需要直接找到这个节点
public void remove(int key){
ListNode cur = this.head;
while (cur!=null) {
if(cur.val == key) {//这里分两种情况
if(cur == head) {//1.cur等于头结点
head = head.next;
head.prev = null;//手动置为空
}else {//2.cur不等于头结点
cur.prev.next = cur.next;
if(cur.next!=null) {
//中间位置
cur.next.prev = cur.prev;
}else {//尾巴位置
last = last.prev;
}
}
return;
}else {
cur = cur.next;
}
}
}
//删除所有值为key的节点
public void removeAllKey(int key){
ListNode cur = this.head;
while (cur != null) {
if (cur.val == key) {
if (cur == head) {
head = head.next;
if (head != null) {
head.prev = null;
} else {
last = null;
}
} else {
cur.prev.next = cur.next;
if (cur.next != null) {
//中间位置
cur.next.prev = cur.prev;
} else {
last = last.prev;
}
}
//return;
}
cur = cur.next;
}
}
public void clear(){
while (head!=null) {
ListNode curNext = head.next;
head.next = null;
head.prev = null;
head = curNext;
}
last = null;
}
}双向链表增删添改的实现
public class TestDemo {
public static void main(String[] args) {
DoubleLinkedList doubleLinkedList = new DoubleLinkedList();
doubleLinkedList.addLast(12);
doubleLinkedList.addLast(13);
doubleLinkedList.addLast(14);
doubleLinkedList.addLast(15);
doubleLinkedList.addLast(16);
doubleLinkedList.display();
System.out.println("=================");
doubleLinkedList.addIndex(3,99);
doubleLinkedList.display();
}
}带傀儡节点的双向链表的实现
class ListNode{
public int val;
public ListNode next;
public ListNode prev;
public ListNode(int val) {
this.val = val;
}
}
public class DoubleLinkedList {//带傀儡节点的双链表
public ListNode dummyHead;//虚拟节点
public ListNode last;//尾节点
public DoubleLinkedList() {
this.dummyHead = new ListNode(-1);//傀儡节点
}
//打印单链表
public void display() {
ListNode cur = this.dummyHead.next;
//引用cur代替head，head等于傀儡节点下一个节点
while (cur != null) {
System.out.print(cur.val + " ");
cur = cur.next;
}
System.out.println();
}
//得到单链表的长度
public int size() {
int count = 0;//记录节点个数
ListNode cur = this.dummyHead.next;
while (cur != null) {
count++;
cur = cur.next;
}
return count;
}
//头插法
public void addFirst(int data) {
ListNode node = new ListNode(data);
//第一次插入一个节点都没有的情况
if (this.dummyHead.next == null) {
node.prev = dummyHead;
this.dummyHead.next = node;
this.last = node;
return;
} else {
//新插入的节点和他前后节点连接
node.next = this.dummyHead.next;
node.prev = this.dummyHead;
this.dummyHead.next.prev = node;
this.dummyHead.next = node;
}
}
//尾插法
public void addLast(int data) {
ListNode node = new ListNode(-1);
//判断头节点是否为空
if (this.dummyHead.next == null && this.last.next == null) {
this.dummyHead.next = node;
node.prev = this.dummyHead;
this.last = node;
return;
} else {
this.last.next = node;
node.prev = last;
this.last = node;
}
}
//任意位置插入,第一个数据节点为0号下标
public void addIndex(int index, int data) {
ListNode node = new ListNode(data);
if(index<0 || index>size()){
System.out.println("index位置不合法");
return;
}else {
if(index == 0) {
addFirst(data);
}
if(index == size()) {
addLast(data);
}else {
//中间位置的时候
ListNode cur = searchIndex(index);
node.next = cur;
cur.prev.next = node;
node.prev = cur.prev;
cur.prev = node;
}
}
}
//创建个方法找到cur的位置
public ListNode searchIndex(int index) {
//先找到cur的位置
ListNode cur = this.dummyHead.next;
while (index!=0) {
cur = cur.next;
index--;
}
return cur;
}
//查找是否包含关键字key是否在单链表当中
public boolean contains(int key){
ListNode cur = this.dummyHead.next;
while (cur!=null) {
if(cur.val == key) {
return true;
}
cur = cur.next;
}
return false;
}
//删除第一次出现关键字为key的节点
//单链表中删除第一次出现的关键字需要找到关键字前驱
//双链表只需要直接找到这个节点
public void remove(int key){
ListNode cur = this.dummyHead.next;
if(cur.val == key){//有两种情况 cur=head或者cur不等于head
if(cur == this.dummyHead.next) {//cur==head时
this.dummyHead.next = this.dummyHead.next.next;
this.dummyHead.next.next.prev = null;
}else {//cur不等于head又有两种情况
//1.cur在中间位置2.cur在最后的位置
cur.prev.next = cur.next;
//判断是不是最后一个节点
//要删除的节点不是最后一个节点
if(cur.next!=null){
cur.next.prev = cur.prev;
}else {
this.last = cur.prev;
}
}
return;
}else {
cur = cur.next;
}
}
//删除所有值为key的节点
public void removeAllKey(int key){
ListNode cur = this.dummyHead.next;
while (cur!=null) {
if(cur.val == key){
if(cur == this.dummyHead.next) {
this.dummyHead.next = this.dummyHead.next.next;
this.dummyHead.next.prev = null;
}else {
cur.prev.next = cur.next;
//判断如果是最后一个节点
if(cur.next == null) {
this.last = cur.prev;
}else {
cur.next.prev = cur.prev;
}
}
}
cur = cur.next;
}
}
public void clear(){
ListNode cur = this.dummyHead.next;
ListNode curNext = cur.next;
while (cur!=null) {
cur.prev = null;
cur.next = null;
cur = curNext;
}
this.dummyHead = null;
this.last = null;
}
}
