无头双向链表的实现

1.头插法

public void addFirst(int data) {  //头插
        DLinkedNode newNode = new DLinkedNode(data);//加入的新节点
        DLinkedNode next = head.next;
        newNode.next = next;
        next.prev = newNode;
        head.next = newNode;
        newNode.prev = head;
    }

2.尾插法

public void addLast(int data) {//尾插
        DLinkedNode newNode = new DLinkedNode(data);//新插入的节点
        DLinkedNode prev = head.prev;
        newNode.next = head;
        head.prev = newNode;
        newNode.prev = prev;
        prev.next = newNode;
    }

3.任意位置插入,第一个数据节点为0号下标

public void addIndex(int index,int data) {//任意位置插入
        int size = size();
        if(index < 0 || index > size){
            return;
        }
        if(index == 0){
            addFirst(data);
            return;
        }
        if(index == size) {
            addLast(data);
            return;
        }
        DLinkedNode next = getPos(index);
        DLinkedNode prev = next.prev;
        DLinkedNode newNode = new DLinkedNode(data);
        prev.next = newNode;
        newNode.prev = prev;
        next.prev = newNode;
        newNode.next = next;
    }

这里用到的计算链表长度的方法：

public int size(){
        int size = 0;
        for(DLinkedNode cur = head.next; cur != head; cur = cur.next) {
            size++;
        }
        return size;
    }

和查找链表中某一位置的方法：

public DLinkedNode getPos(int index) {
        DLinkedNode cur = head.next;
        for(int i = 0; i < index; i++){
            cur = cur.next;
        }
        return cur;
    }

4.查找是否包含关键字key是否在链表当中

public boolean contains(int key) {//查找是否包含关键字key的节点
        for(DLinkedNode cur = head.next; cur != head; cur = cur.next) {
            if(cur.val == key){
                return true;
            }
        }
        return false;
    }

5.删除第一次出现关键字为key的节点

public void remove(int key){
        DLinkedNode toRemove = find(key);
        if(toRemove == null) {
            return;
        }
        DLinkedNode prev = toRemove.prev;
        DLinkedNode next = toRemove.next;
        prev.next = next;
        next.prev = prev;
    }

这里用到查找关键字key在链表中的位置的方法：

public DLinkedNode find(int key) {
        for(DLinkedNode cur = head.next; cur != head; cur = cur.next) {
            if(cur.val == key){
                return cur;
            }
        }
        return null;
    }

6.删除所有值为key的节点

public void removeAll(int key){
        while (true){
            DLinkedNode toRmove = find(key);
            if(toRmove == null){
                return;
            }
            DLinkedNode prev = toRmove.prev;
            DLinkedNode next = toRmove.next;
            prev.next = next;
            next.prev = prev;
        }
    }

7.打印链表

public void display(){
        System.out.print("正向:[");
        for(DLinkedNode cur = head.next; cur != head; cur = cur.next){
            System.out.print(cur.val);
            if(cur.next != head){
                System.out.print(",");
            }
        }
        System.out.println("]");
        System.out.println("反向:[");
        for(DLinkedNode cur = head.prev; cur != head; cur = cur.prev){
            System.out.print(cur.val);
            if(cur.prev != head){
                System.out.print(",");
            }
        }
        System.out.println("]");
    }

8.清空链表

public void clear(){
        head.next = head;
        head.prev = head;
    }