回顾
最基础的动态数据结构
Linked List
- 数据存储在节点(Node)中:
class Node{
E e;
Node next;
}
最后一个Node的下一个Node为null
- 优点 : 真正的动态 不需要处理固定的容量的问题
- 缺点: 丧失了随机访问的能力
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();
}
}
}
在链表头添加元素
//为链表头添加元素
public void addFirst(E e){
// Node node = new Node(e);
// node.next = head;
// head = node;
head = new(e,head);
size ++;
}
在链表中间添加元素
prev:插入节点之前的那一个节点
//在链表index(0-based)位置添加元素e
public void add(index,e){
if(index < 0 || index > size)
throw new IllegealArgumentException("error");
if(index == 0)
addFirst(e);
else{
Node prev = head;
for(int i = 0;i < index -1 ; i ++)
prev = prev.next;
Node node = new Node(e);
node.next = prev.next;
prev.next = node.next;
prev.next = new Node(e,prev.next);
size ++;
}
}
//在末尾添加
public void addLast(E e){
add(size ,e);
}
在链表中添加虚拟头结点
dummyHead: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;
}
// 获取链表中的元素个数
public int getSize(){
return size;
}
// 返回链表是否为空
public boolean isEmpty(){
return size == 0;
}
// 在链表的index(0-based)位置添加新的元素e
// 在链表中不是一个常用的操作，练习用：）
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 ++;
}
// 在链表头添加新的元素e
public void addFirst(E e){
add(0, e);
}
// 在链表末尾添加新的元素e
public void addLast(E e){
add(size, e);
}
}
链表的查询遍历和修改
//bianli
public E get(int index){
if(index < 0 || index >= size){
throw new IllegalArgumentException("error!");
}
Node cur = dummyHead.next;
for(int i = 0 ; i < index; i ++){
cur = cur.next;
}
return cur.e;
}
//或得链表的第一个元素
public E getFirst(){
return get(0);
}
//
public E getLast(){
return get(size - 1);
}
//查找链表中是否存在元素e
//查找链表中是否存在元素e
public boolean contains(E e){
Node cur = dummyHead.next;
while(cur != null){
if(cur.e.equals(e))
return true;
cur = cur.next;
}
retrun false;
}
遍历所有的元素
// 修改链表的第index(0-based)个位置的元素为e
// 在链表中不是一个常用的操作，练习用：）
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;
}
// 查找链表中是否有元素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;
}
@Override
public String toString(){
StringBuilder res = new StringBuilder();
// Node cur = dummyHead.next;
// while(cur != null){
// res.append(cur + "->");
// cur = cur.next;
// }
for(Node cur = dummyHead.next ; cur != null ; cur = cur.next)
res.append(cur + "->");
res.append("NULL");
return res.toString();
}
}
链表中删除元素
// 从链表中删除元素e
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 --;
}
}
@Override
public String toString(){
StringBuilder res = new StringBuilder();
Node cur = dummyHead.next;
while(cur != null){
res.append(cur + "->");
cur = cur.next;
}
res.append("NULL");
return res.toString();
}
链表的时间复杂度分析
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();
}
@Override
public String toString(){
StringBuilder res = new StringBuilder();
res.append("Stack: top ");
res.append(list);
return res.toString();
}
public static void main(String[] args) {
LinkedListStack<Integer> stack = new LinkedListStack<>();
for(int i = 0 ; i < 5 ; i ++){
stack.push(i);
System.out.println(stack);
}
stack.pop();
System.out.println(stack);
}
}
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;
}
@Override
public String toString(){
StringBuilder res = new StringBuilder();
res.append("Queue: front ");
Node cur = head;
while(cur != null) {
res.append(cur + "->");
cur = cur.next;
}
res.append("NULL tail");
return res.toString();
}
public static void main(String[] args){
LinkedListQueue<Integer> queue = new LinkedListQueue<>();
for(int i = 0 ; i < 10 ; i ++){
queue.enqueue(i);
System.out.println(queue);
if(i % 3 == 2){
queue.dequeue();
System.out.println(queue);
}
}
}
}
