4-1 什么是链表
为什么链表很重要
- 链表:真正的动态数据结构
- 最简单的动态数据结构
- 更深入的理解引用(或者指针)
- 更深入的理解递归
- 辅助组成其他数据结构
链表
数据存储在"节点(Node)中
class Node {
E e;
Node next;
}
优点:真正的动态,不需要处理固定容量的问题
缺点:丧失了随机访问的能力
数组与链表的对比
数组 |
链表 |
数组最好用于索引有语意的情况。scores[2] |
链表不适合索引有语意的情况 |
支持快速查询 |
动态 |
public class LinkedList<E> {
private class Node{
public E e;
public Node next;
public Node(E e, Node next){
this.e = e;
this.next = next;
}
public Node(E e){
this(e, null);
}
public Node(){
this(null, null);
}
}
4-2 链表Linked List
在链表头添加元素
public void addFirst(E e){
head = new Node(e, head);
size ++;
}
在链表中间和末尾添加元素
public void add(int index, E e){
if(index < 0 || index > size)
throw new IllegalArgumentException("Add failed. Illegal index.");
if(index == 0)
addFirst(e);
else{
Node prev = head;
for(int i = 0 ; i < index - 1 ; i ++)
prev = prev.next;
prev.next = new Node(e, prev.next);
size ++;
}
}
public void addLast(E e){
add(size, e);
}
4-3 使用链表的虚拟头结点
public class LinkedList<E> {
private class Node{
public E e;
public Node next;
public Node(E e, Node next){
this.e = e;
this.next = next;
}
public Node(E e){
this(e, null);
}
public Node(){
this(null, null);
}
@Override
public String toString(){
return e.toString();
}
}
private Node dummyHead;
private int size;
public LinkedList(){
dummyHead = new Node();
size = 0;
}
public int getSize(){
return size;
}
public boolean isEmpty(){
return size == 0;
}
public void add(int index, E e){
if(index < 0 || index > size)
throw new IllegalArgumentException("Add failed. Illegal index.");
Node prev = dummyHead;
for(int i = 0 ; i < index ; i ++)
prev = prev.next;
prev.next = new Node(e, prev.next);
size ++;
}
public void addFirst(E e){
add(0, e);
}
public void addLast(E e){
add(size, e);
}
}
4-4 链表的遍历,查询和修改
public E get(int index){
if(index < 0 || index >= size)
throw new IllegalArgumentException("Get failed. Illegal index.");
Node cur = dummyHead.next;
for(int i = 0 ; i < index ; i ++)
cur = cur.next;
return cur.e;
}
public E getFirst(){
return get(0);
}
public E getLast(){
return get(size - 1);
}
public void set(int index, E e){
if(index < 0 || index >= size)
throw new IllegalArgumentException("Set failed. Illegal index.");
Node cur = dummyHead.next;
for(int i = 0 ; i < index ; i ++)
cur = cur.next;
cur.e = e;
}
public boolean contains(E e){
Node cur = dummyHead.next;
while(cur != null){
if(cur.e.equals(e))
return true;
cur = cur.next;
}
return false;
}
4-5 从链表中删除元素
public E remove(int index){
if(index < 0 || index >= size)
throw new IllegalArgumentException("Remove failed. Index is illegal.");
Node prev = dummyHead;
for(int i = 0 ; i < index ; i ++)
prev = prev.next;
Node retNode = prev.next;
prev.next = retNode.next;
retNode.next = null;
size --;
return retNode.e;
}
public E removeFirst(){
return remove(0);
}
public E removeLast(){
return remove(size - 1);
}
public void removeElement(E e){
Node prev = dummyHead;
while(prev.next != null){
if(prev.next.e.equals(e))
break;
prev = prev.next;
}
if(prev.next != null){
Node delNode = prev.next;
prev.next = delNode.next;
delNode.next = null;
size --;
}
}
链表的时间复杂度分析
添加操作 |
时间复杂度 |
addLast(e) |
O(n) |
addFirst(e) |
O(1) |
add(index,e) |
O(n/2)=O(n) |
综合 |
O(n) |
删除操作 |
时间复杂度 |
removeLast(e) |
O(n) |
removeFirst(e) |
O(1) |
remove(index,e) |
O(n/2)=O(n) |
综合 |
O(n) |
修改操作 |
时间复杂度 |
set(index,e) |
O(n) |
查找操作 |
时间复杂度 |
get(index) |
O(n) |
contains(e) |
O(n) |
4-6 使用链表实现栈
public class LinkedListStack<E> implements Stack<E> {
private LinkedList<E> list;
public LinkedListStack(){
list = new LinkedList<>();
}
@Override
public int getSize(){
return list.getSize();
}
@Override
public boolean isEmpty(){
return list.isEmpty();
}
@Override
public void push(E e){
list.addFirst(e);
}
@Override
public E pop(){
return list.removeFirst();
}
@Override
public E peek(){
return list.getFirst();
}
4-7 带有尾指针的链表:使用链表实现队列
public class LinkedListQueue<E> implements Queue<E> {
private class Node{
public E e;
public Node next;
public Node(E e, Node next){
this.e = e;
this.next = next;
}
public Node(E e){
this(e, null);
}
public Node(){
this(null, null);
}
@Override
public String toString(){
return e.toString();
}
}
private Node head, tail;
private int size;
public LinkedListQueue(){
head = null;
tail = null;
size = 0;
}
@Override
public int getSize(){
return size;
}
@Override
public boolean isEmpty(){
return size == 0;
}
@Override
public void enqueue(E e){
if(tail == null){
tail = new Node(e);
head = tail;
}
else{
tail.next = new Node(e);
tail = tail.next;
}
size ++;
}
@Override
public E dequeue(){
if(isEmpty())
throw new IllegalArgumentException("Cannot dequeue from an empty queue.");
Node retNode = head;
head = head.next;
retNode.next = null;
if(head == null)
tail = null;
size --;
return retNode.e;
}
@Override
public E getFront(){
if(isEmpty())
throw new IllegalArgumentException("Queue is empty.");
return head.e;
}
}