【链表】实现单链表的逆序

public class Main {

    // 就地逆序法
    public Node reverse(Node head) {
        // no need to reverse
        if (head == null || head.next == null || head.next.next == null) {
            return head;
        }

        // pointer
        Node pre = head;
        Node cur = head.next;
        Node nex = head.next.next;

        while (nex != null) {
            if (cur == head.next)  // the first node's next node is null
            {
                cur.next = null;
            } else {
                cur.next = pre;
            }

            pre = cur;
            cur = nex;
            nex = nex.next;
        }

        cur.next = pre;
        head.next = cur;

        return head;
    }

    // 插入法
    public Node reverse2(Node head) {
        if (head == null || head.next == null) {
            return head;
        }

        Node p1 = head.next;

        Node p = null;

        while (p1.next != null) {
            p = p1.next;
            p1.next = p.next;
            p.next = head.next;
            head.next = p;
        }

        return head;
    }

    public Node createListNodes() {
        Node node7 = new Node(7, null);
        Node node6 = new Node(6, node7);
        Node node5 = new Node(5, node6);
        Node node4 = new Node(4, node5);
        Node node3 = new Node(3, node4);
        Node node2 = new Node(2, node3);
        Node node1 = new Node(1, node2);
        Node head = new Node(0, node1); // head pointer

        return head;
    }

    public static void main(String[] args) {
        Main main = new Main();
        Node node = main.reverse(main.createListNodes());

        if (node == null) {
            System.out.println("head is null");
            return;
        }

        while (node.next != null) {
            System.out.println(node.next.data);
            node = node.next;
        }

        Node node2 = main.reverse2(main.createListNodes());

        if (node2 == null) {
            System.out.println("head is null");
            return;
        }

        while (node2.next != null) {
            System.out.println(node2.next.data);
            node2 = node2.next;
        }
    }

}