Java链表在第一个位置插入节点

Question

我如何修改此代码，将节点从第二个位置插入到第一个位置？

static void insertAtMid(int x)
    {

        if (head == null)
            head = new Node(x);
        else {

            Node newNode = new Node(x);

            Node ptr = head;
            int len = 0;


            while (ptr != null) {
                len++;
                ptr = ptr.next;
            }


            int count = (len >=1)? 1 : 0;
            ptr = head;


            while (count-- > 1)
                ptr = ptr.next;


            newNode.next = ptr.next;
            ptr.next = newNode;
        }
    }

    static void display()
    {
        Node temp = head;
        while (temp != null)  
        {
            System.out.print(temp.data + " ");
            temp = temp.next;
        }
    }

    public static void main (String[] args)  
    {  

        head = null;
        head = new Node(23);
        head.next = new Node(45);
        head.next.next = new Node(12);
        head.next.next.next = new Node(67);

        System.out.println("Linked list before "+
                           "insertion: ");
        display();

        int x = 55;
        insertAtMid(x);

        System.out.println("\nLinked list after"+
                           " insertion: ");
        display();
    }  

Answer 1

要在链表的开头插入新节点，您所要做的就是创建一个新节点，然后将其 next 值设置为当前头:

Node newHead = new Node(x);
newHead.next = head;

此时，新的头是newHead，它已经被插入到链表的开头了。