数据结构---链表(java)

目录

1. 链表

2. 创建Node

3. 增加

4. 获取元素

5. 删除

6. 遍历链表

7. 查找元素是否存在

8. 链栈的实现

9. 链队的实现 

---

1. 链表

• 数据存放在"Node"结点中

优点：不用考虑扩容和缩容的问题，实现了动态存储数据

缺点：没有随机访问的能力

2. 创建Node

先创建一个MyLinkedList类，初始化Node结点内部类

private class Node {
        private T val;
        private Node next;

        public Node() {
            this.val = null;
            this.next = null;
        }

        public Node(T val) {
            this.val = val;
            this.next = null;
        }
    }

3. 增加

<1> 在头部添加

public void addHead(T val) {
        Node node = new Node(val);
        node.next = this.header;
        this.header = node;
        this.size++;
    }

<2> 在尾部添加

public void tail(T val) {
        Node node = new Node(val);
        this.size++;
        if(header.next==null){
            this.header=node;
            return;
        }
        Node cur = header;
        while (cur.next!=null){
            cur = cur.next;
        }
        cur.next=node;
    }

<3> 在任意位置添加

public void add(int index, T val) {
        if (index < 0 || index > this.size) {
            throw new IllegalArgumentException("index is invalid");
        }
        //要插入的结点
        Node node = new Node(val);
        //新建一个虚拟头节点
        Node dummyHead = new Node(null);
        dummyHead.next = header;
        Node pre = dummyHead;
        //找到待插入位置的前一个结点
        for (int i = 0; i < index; i++) {
            pre = pre.next;
        }
        node.next = pre.next;
        pre.next = node;
        //更新头节点
        header = dummyHead.next;
        this.size++;
    }

4. 获取元素

<1> 获取头部元素

public T getHead() {
        if (isEmpty()) {
            return null;
        }
        return header.val;
}

<2> 获取尾部元素

public T getHail() {
        if (isEmpty()) {
            return null;
        }
        Node cur = this.header;
        while (cur.next != null) {
            cur = cur.next;
        }
        return cur.val;
    }

<3> 获取任意节点元素

public T get(int index) {
        if (index < 0 || index > this.size) {
            throw new IllegalArgumentException("index is invalid");
        }
        Node cur = this.header;
        int i = 1;
        while (i <= index) {
            cur = cur.next;
            i++;
        }
        return cur.val;
    }

5. 删除

<1> 通过下标删除结点

public Optional removeByIndex(int index){
        if(index<0||index>=this.size){
            return Optional.empty();
        }
        //判断是否是头结点
        //使用虚拟头节点
        Node dummyNode = new Node(null);
        dummyNode.next = header;
        Node pre = dummyNode;
        int i=1;
        //寻找要删除的结点
        while(i<=index){
            pre = pre.next;
            i++;
        }
        //改变指针指向
        Node delNode = pre.next;
        pre.next = delNode.next;
        delNode.next = null;
        this.size--;
        this.header = dummyNode.next;
        return Optional.of(delNode.val);
    }

<2> 通过值删除结点

public void removeByVal(T val){
        if(isEmpty()){
            return;
        }
        Node dummyNode = new Node(null);
        dummyNode.next = header;
        Node pre = dummyNode;
        while(pre.next!=null){
            Node cur = pre.next;
            if(cur.val.equals(val)){
                pre.next=cur.next;
                cur.next=null;
                size--;
            }else {
                pre = pre.next;
            }
        }
        header = dummyNode.next;
    }

<3> 不使用虚拟头结点删除元素

public void removeWithoutDummyHead(T val){
        while(this.header!=null&&this.header.val.equals(val)){
            this.header = this.header.next;
            this.size--;
        }
        if(this.header==null){
            return;
        }
        //此时头节点一定不是要删除的结点
        Node pre = this.header;
        while(pre.next!=null){
            if(pre.next.val.equals(val)){
                pre.next = pre.next.next;
                this.size--;
            }else{
                pre = pre.next;
            }
        }
}

6. 遍历链表

重写toString()方法，将他拼接成链表的样子

@Override
    public String toString() {
        //创建一个临时结点
        Node cru = header;
        StringBuffer sb = new StringBuffer();
        while (cru != null) {
            sb.append(cru.val + "--->");
            cru = cru.next;
        }
        sb.append("Null");
        return sb.toString();
    }

7. 查找元素是否存在

public boolean contains(T val) {
        Node res = new Node(val);
        Node cur = header;
        for (int i = 0; i < this.size; i++) {
            if (res.val.equals(cur.val)) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

8. 链栈的实现

public interface Stack {
    void push(T element);
    T pop();
    int getSize();
    boolean isEmpty();
    T peek();
}

public class LinkedStack implements Stack {

    private MyLinkedList data;

    public LinkedStack(MyLinkedList data) {
        this.data = data;
    }

    @Override
    public void push(T element) {
        this.data.addTail(element);
    }

    @Override
    public T pop() {
        Optional optional = this.data.removeByIndex(0);
        if(optional.isPresent()){
            return optional.get();
        }
        return null;
    }

    @Override
    public int getSize() {
        return this.data.getSize();
    }

    @Override
    public boolean isEmpty() {
        return this.data.isEmpty();
    }

    @Override
    public T peek() {
        return this.data.getHead();
    }
}

9. 链队的实现 

public interface Queue{
    void offer(T ele);
    T poll();
    boolean isEmpty();
    int getSize();
    T getFront();
}

public class LinkedQueue implements Queue {
    private MyLinkedList data;

    public LinkedQueue(MyLinkedList myLinkedList) {
        this.data = myLinkedList;
    }

    @Override
    public void offer(Object ele) {
        this.data.addTail(ele);
    }

    @Override
    public Object poll() {
        return this.data.removeByIndex(0);
    }

    @Override
    public boolean isEmpty() {
        return this.data.isEmpty();
    }

    @Override
    public int getSize() {
        return this.data.getSize();
    }

    @Override
    public Object getFront() {
        return this.data.getHead();
    }
}