一、实现MyDLinkedList（双向链表）
java
package LinkedList;
public class MyDLinkedList {
//首先我们要创建节点（因为双向链表和单向链表的节点不一样！！）
static class Node{
public String val;
public Node prev = null;
public Node next = null;
//给一个构造方法
public Node(String val) {
this.val = val;
}
}
//表示整个链表，此处不引入傀儡节点，使用Null表示空的链表
public Node head = null;
//为了方便后续的尾插曹祖
public Node tail = null;
//给一个toStirng的打印
@Override
public String toString() {
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append("[");
//进行链表的遍历
for(Node cur = head;cur!= null ;cur = cur.next){
stringBuilder.append(cur.val);
if(cur.next != null) {
stringBuilder.append(",");
}
}
stringBuilder.append("]");
return stringBuilder.toString();
}
//接下来来实现一些双向链表的核心操作
//1.实现头插操作
public void addFirst(String val){
Node newNode = new Node(val);
//首先判断链表是否为空的情况
if(head == null){
head = newNode;
tail = newNode;
}else {
//再来看看一般情况
newNode.next = head;
head. prev = newNode;
//2.让head指向新节点
head = newNode;
}
}
//2.实现链表的尾插操作
public void addLast(String val){
Node newNode = new Node(val);
//1.首先判断链表为空的情况，可知与头插操作一样
if(head == null){
head = newNode;
tail = newNode;
}else {
//2.考虑一般情况
tail.next = newNode;
newNode.prev = tail;
tail = newNode;
}
}
//实现链表长度的计算
public int size(){
int size =0;
for(Node cur = head;cur != null;cur = cur.next){
size++;
}
return size;
}
//3.实现双向链表的按位置插入
public void add(int index,String val){
int size = size();
//1.首先判断index的值是否合法
if( index < 0 || index > size ){
throw new IndexOutOfBoundsException("Index:"+index+",Size:"+size);
}
//2.判断特殊位置
if(index ==0 ){
//此时就是头插操作
addFirst(val);
return;
}
if(index== size){
//此时就是尾插
addLast(val);
return;
}
//3.进行一般的插入
//先找到要插入节点的前一个节点
Node prev = head;
for(int i =0;i<index-1;i++){
prev = prev.next;
}
//此时我们已经找到了要插入节点的前一个节点
Node newNode = new Node(val);
Node next = prev.next;
//首先建立新节点与上一个节点之间的关系
prev.next = newNode;
newNode.prev = prev;
//再建立新节点与下一个节点之间的关系
newNode.next = next;
next.prev = newNode;
}
//4.实现包含查找操作
public Boolean contains(String val){
for (Node cur = head ; cur != null;cur = cur.next){
if(cur.val.equals(val)) {
return true;
}
}
return false;
}
//5.查找元素，返回该元素的下标，如果没有找到，返回-1
public int indexOf(String val){
int index =0;
for (Node cur = head;cur != null;cur =cur.next){
if(cur.val.equals(val)){
return index;
}
index++;
}
return -1;
}
//6.头删
public void removeFirst(){
//1.首先考虑是否为空链表
if(head == null){
return;//空链表无法进行删除操作
}
//2.考虑只有一个节点的情况
if(head.next == null){
head = null;
tail = null;
return;
}
//3.考虑一般情况
head = head.next;
head.prev = null;
}
//7.尾部删除
public void removeLast(){
//1.考虑空链表
if (head == null){
return;
}
//2.考虑只有一个节点
if(head.next == null){
head = null;
tail = null;
return;
}
//3.考虑一般情况
tail = tail.prev;
tail.next = null;
}
//8.指定位置删除
public void remove(int index){
int size = size();
//对index做判断
if(index <0 || index >= size){
throw new IndexOutOfBoundsException("index:"+index+",size:"+size);
}
//2.如果是删除index=0
if(index ==0){
removeFirst();
return;
}
if(index ==size-1){
removeLast();
return;
}
//3.考虑一般情况的删除
//先找到前一个节点
Node prev = head;
for(int i =0;i<index-1;index++){
prev = prev.next;
}
Node toRemove = prev.next;
Node next = toRemove.next;
//4.进行删除操作
prev.next = next;
next.prev =prev;
}
//9.指定值删除
public void remove(String val){
//1.首先考虑空的链表
if(head == null){
return ;
}
//2.判定头删/尾删操作
if(val.equals(head.val)){
removeFirst();
return;
}
if(val.equals(tail.val)){
removeLast();
return;
}
//3.一般情况 先找到前一个节点
Node toRemove = head;
for (;toRemove!=null;toRemove= toRemove.next){
if(toRemove.val.equals(val)){
break;
}
}
//循环之外有两种情况一种是找到了打破循环 另一种是循环走完了！
if(toRemove == null){
return ;
}
Node prev = toRemove.prev;
Node next = toRemove.next;
prev.next = next;
next.prev = prev;
}
//10.链表的清空操作
public void clear(){
head = null;
tail = null;
}
public static void test(){
MyDLinkedList list = new MyDLinkedList();
list.addFirst("a");
list.addFirst("b");
list.addFirst("c");
System.out.println(list);
}
public static void test1(){
MyDLinkedList list = new MyDLinkedList();
list.addLast("c");
list.addLast("b");
list.addLast("a");
System.out.println(list);
}
public static void test3(){
MyDLinkedList list = new MyDLinkedList();
list.addFirst("a");
list.addFirst("a");
list.addFirst("a");
list.addFirst("a");
list.add(0,"b");
list.add(2,"c");
System.out.println(list);
}
public static void test4(){
MyDLinkedList list = new MyDLinkedList();
list.addFirst("a");
list.addFirst("a");
list.addFirst("a");
list.addFirst("a");
list.add(0,"b");
list.add(2,"c");
System.out.println(list);
System.out.println(list.indexOf("a"));
System.out.println(list.contains("b"));
System.out.println(list.contains("d"));
}
public static void test5() {
MyDLinkedList list = new MyDLinkedList();
list.addFirst("a");
list.addFirst("a");
list.addFirst("a");
list.addFirst("a");
list.add(0, "b");
list.add(2, "c");
System.out.println(list);
list.removeFirst();
list.removeFirst();
System.out.println(list);
}
public static void test6() {
MyDLinkedList list = new MyDLinkedList();
list.addFirst("a");
list.addFirst("a");
list.addFirst("a");
list.addFirst("a");
list.add(0, "b");
list.add(2, "c");
System.out.println(list);
list.removeLast();
list.removeLast();
System.out.println(list);
}
public static void test7() {
MyDLinkedList list = new MyDLinkedList();
list.addFirst("a");
list.addFirst("a");
list.addFirst("a");
list.addFirst("a");
list.add(0, "b");
list.add(2, "c");
System.out.println(list);
list.remove(1);
list.remove(4);
System.out.println(list);
}
public static void test8() {
MyDLinkedList list = new MyDLinkedList();
list.addLast("a");
list.addLast("b");
list.addLast("c");
System.out.println(list);
list.remove("a");
System.out.println(list);
}
public static void main(String[] args) {
// test();
// test1();
//test3();
// test4();
//test5();
//test6();
//test7();
//test8();
}
}