目录
1、链表
1.1 链表的概念及结构
链表是一种物理存储结构上非连续存储结构,数据元素的逻辑顺序是通过链表中的引用链接次序实现的。实际中链表的结构非常多样,以下常见的链表结构:
1. 单向或者双向
2. 带头或者不带头
3. 循环或者非循环
我们主要掌握以下两种结构:
- 无头单向非循环链表:结构简单,一般不会单独用来存数据。实际中更多是作为其他数据结构的子结构,如哈希桶、图的邻接表等等。
- 无头双向链表:在Java的集合框架库中LinkedList底层实现就是无头双向循环链表。
1.2 链表的实现
这里我们实现的是无头单向非循环链表:
//无头单向非循环链表实现
public class MySingleList implements IList{
static class ListNode {
public int val;
public ListNode next;
public ListNode(int val) {
this.val = val;
}
}
public ListNode head;
public void CreateLinkedList() {
ListNode node1 = new ListNode(10);
ListNode node2 = new ListNode(20);
ListNode node3 = new ListNode(30);
ListNode node4 = new ListNode(40);
node1.next = node2;
node2.next = node3;
node3.next = node4;
this.head = node1;
}
@Override
public void addFirst(int data) {
ListNode node = new ListNode(data);
if (this.head == null) {
this.head = node;
}else {
node.next = this.head;
this.head = node;
}
}
@Override
public void addLast(int data) {
ListNode node = new ListNode(data);
ListNode cur = head;
if (this.head == null) {
this.head = node;
return;
}
while (cur.next!=null) {
cur = cur.next;
}
cur.next = node;
node.next = null;
}
@Override
public void addIndex(int index, int data) throws Indexillegal{
if(index < 0||index > size()){
//抛自定义异常
throw new Indexillegal("插入下标异常:"+index);
}
if (index==0) {
addFirst(data);
}
if (index == size()) {
addLast(data);
}
ListNode node = new ListNode(data);
ListNode cur = searchPre(index);
node.next=cur.next;
cur.next=node;
}
private ListNode searchPre(int index) {
ListNode cur = head;
int count = 0;
while (count != index-1) {
cur=cur.next;
count++;
}
return cur;
}
@Override
public boolean contains(int key) {
ListNode cur = head;
while (cur!=null) {
if (cur.val==key) {
return true;
}
cur = cur.next;
}
return false;
}
@Override
public void remove(int key) {
if (this.head == null){
return;
}
if (this.head.val == key) {
this.head=head.next;
return;
}
ListNode cur = DelPrv(key);
if (cur == null) {
System.out.println("要删除的元素不存在");
}else {
ListNode del = cur.next;
cur.next=del.next;
}
}
private ListNode DelPrv(int key) {
ListNode cur = head;
while (cur.next!=null) {
if (cur.next.val==key) {
return cur;
}
cur = cur.next;
}
return null;
}
@Override
public void removeAllKey(int key) {
if (this.head == null) {
return;
}
ListNode prv = head;
ListNode cur = head.next;
while (cur != null) {
if (cur.val == key) {
prv.next=cur.next;
cur=cur.next;
}else {
prv = cur;
cur = cur.next;
}
}
if (this.head.val == key) {
this.head=this.head.next;
}
}
@Override
public int size() {
ListNode cur = head;
int count = 0;
while (cur!=null) {
count++;
cur = cur.next;
}
return count;
}
@Override
public void clear() {
ListNode cur = head;
while (cur!=null) {
ListNode curNext = cur.next;
cur.next = null;
cur = curNext;
}
head = null;
}
@Override
public void display() {
ListNode cur = head;
while (cur!=null) {
System.out.print(cur.val+" ");
cur = cur.next;
}
System.out.println();
}
//从指定位置打印
public void display(ListNode node) {
ListNode cur = node;
while (cur!=null) {
System.out.print(cur.val+" ");
cur = cur.next;
}
System.out.println();
}
}
其中自定义异常Indexillegal:
public class Indexillegal extends RuntimeException{
public Indexillegal(String msg) {
super(msg);
}
}
2、LinkedList的模拟实现
LinkedList底层实现就是无头双向循环链表,所以下面是对无头双向链表的实现:
//无头双向链表的实现
public class MyLinkedList implements IList{
static class ListNode{
public int val;
public ListNode next;
public ListNode prev;
public ListNode(int val) {
this.val = val;
}
}
public ListNode head;
public ListNode last;
@Override
public void addFirst(int data) {
ListNode listNode = new ListNode(data);
if (head == null) {
head = listNode;
last = listNode;
}else {
listNode.next = head;
head.prev=listNode;
head=listNode;
}
}
@Override
public void addLast(int data) {
ListNode listNode = new ListNode(data);
if (head == null){
head = listNode;
last = listNode;
}else {
last.next=listNode;
listNode.prev=last;
last = listNode;
}
}
@Override
public void addIndex(int index, int data) {
int len = size();
if (index < 0|| index > len) {
System.out.println("插入异常");
return;
}
if (index==0) {
addFirst(data);
return;
}
if (index==len) {
addLast(data);
return;
}
ListNode node = new ListNode(data);
ListNode cur = FindIndex(index);
node.next = cur;
cur.prev.next = node;
node.prev = cur.prev;
cur.prev = node;
}
private ListNode FindIndex(int index) {
ListNode cur = head;
while (index != 0){
cur = cur.next;
index--;
}
return cur;
}
@Override
public boolean contains(int key) {
ListNode cur = head;
while (cur!=null) {
if (cur.val==key) {
return true;
}
cur = cur.next;
}
return false;
}
@Override
public void remove(int key) {
ListNode cur = head;
while (cur != null) {
if (cur.val == key) {
if (cur == head) {
head = head.next;
if (head == null) {
last = null;
}else {
head.prev = null;
}
}else {
cur.prev.next = cur.next;
if (cur.next == null) {
last = last.prev;
}else {
cur.next.prev = cur.prev;
}
}
return;
}else {
cur = cur.next;
}
}
}
@Override
public void removeAllKey(int key) {
ListNode cur = head;
while (cur != null) {
if (cur.val == key) {
if (cur == head) {
head = head.next;
if (head == null) {
last = null;
}else {
head.prev = null;
}
}else {
cur.prev.next = cur.next;
if (cur.next == null) {
last = last.prev;
}else {
cur.next.prev = cur.prev;
}
}
}
cur = cur.next;
}
}
@Override
public int size() {
ListNode cur = head;
int count = 0;
while (cur!=null) {
count++;
cur = cur.next;
}
return count;
}
@Override
public void clear() {
ListNode cur = head;
while (cur != null) {
ListNode curNext = cur.next;
cur.next = null;
cur.prev = null;
cur = curNext;
}
head = null;
last = null;
}
@Override
public void display() {
ListNode cur = head;
while (cur!=null) {
System.out.print(cur.val+" ");
cur = cur.next;
}
System.out.println();
}
}
3、LinkedList的使用
3.1 什么是LinkedList
在集合框架中,LinkedList也实现了List接口,具体如下:
1. LinkedList实现了List接口
2. LinkedList的底层使用了双向链表
3. LinkedList没有实现RandomAccess接口,因此LinkedList不支持随机访问
4. LinkedList的任意位置插入和删除元素时效率比较高,时间复杂度为O(1)
5. LinkedList比较适合任意位置插入的场景
3.2 LinkedList的使用
1. LinkedList的构造
方法 | 解释 |
LinkedList() | 无参构造 |
public LinkedList(Collection<? extends E> c) | 使用其他集合容器中元素构造List |
代码示例:
public static void main(String[] args) {
// 构造一个空的LinkedList
List<Integer> list1 = new LinkedList<>();
List<String> list2 = new java.util.ArrayList<>();
list2.add("JavaSE");
list2.add("JavaWeb");
list2.add("JavaEE");
// 使用ArrayList构造LinkedList
List<String> list3 = new LinkedList<>(list2);
}
2. LinkedList的其他常用方法介绍
方法 | 解释 |
boolean add(E e) | 尾插 e |
void add(int index, E element) | 将 e 插入到 index 位置 |
boolean addAll(Collection<? extends E> c) | 尾插 c 中的元素 |
E remove(int index) | 删除 index 位置元素 |
boolean remove(Object o) | 删除遇到的第一个 o |
E get(int index) | 获取下标 index 位置元素 |
E set(int index, E element) | 将下标 index 位置元素设置为 element |
void clear() | 清空 |
boolean contains(Object o) | 判断 o 是否在线性表中 |
int indexOf(Object o) | 返回第一个 o 所在下标 |
int lastIndexOf(Object o) | 返回最后一个 o 的下标 |
List<E> subList(int fromIndex, int toIndex) | 截取部分 list |
3.3 LinkedList的遍历
遍历方法有:foreach遍历和使用迭代器遍历
代码示例:
public static void main(String[] args) {
LinkedList<Integer> list = new LinkedList<>();
list.add(1); // add(elem): 表示尾插
list.add(2);
list.add(3);
list.add(4);
list.add(5);
list.add(6);
list.add(7);
System.out.println(list.size());
// foreach遍历
for (int e:list) {
System.out.print(e + " ");
}
System.out.println();
// 使用迭代器遍历---正向遍历
ListIterator<Integer> it = list.listIterator();
while(it.hasNext()){
System.out.print(it.next()+ " ");
}
System.out.println();
// 使用反向迭代器---反向遍历
ListIterator<Integer> rit = list.listIterator(list.size());
while (rit.hasPrevious()){
System.out.print(rit.previous() +" ");
}
System.out.println();
}
4、ArrayList和LinkedList的区别
不同点 | ArrayList | LinkedList |
存储空间上 | 物理上一定连续 | 逻辑上连续,但物理上不一定连续 |
随机访问 | 支持O(1) | 不支持:O(N) |
头插 | 需要搬移元素,效率低O(N) | 只需修改引用的指向,时间复杂度为O(1) |
插入 |
空间不够时需要扩容 |
没有容量的概念 |
应用场景 | 元素高效存储+频繁访问 | 任意位置插入和删除频繁 |
总结:以上就是对LinkedList和链表的总结了,注意它与ArrayList的区别,希望能帮到你们!