面试题： 合并两个有序链表

public class Node {
    public Integer value;
    public Node next;
    // 构造
    public Node(){}
    public Node(Integer value) {
        this.value = value;
    }
    public Node(Integer value,Node next) {
        this.value = value;
        this.next = next;
    }

    // 打印链表
    public void print() {
       Node n = this;
       System.out.println("------------------------------------------------");
       while (n != null) {
           System.out.print(n.value);
           n = n.next;
           if (n != null) {
               System.out.print("-->");
           } else {
               System.out.println();
           }
       }
       System.out.println("------------------------------------------------");
    }
}

public class TestNode {
    public static void main(String[] args) {
        Node L1= getL1();
        Node L2= getL2();
        // 1-->2-->4-->9
        L1.print();
        // 3-->5-->6-->10-->13
        L2.print();
    }

    // 获取测试数据L1
    public static Node getL1() {
        Node head = new Node(1,new Node(2,new Node(4,new Node(9))));
        return head;
    }
    // 获取测试数据L2
    public static Node getL2() {
        Node head = new Node(3,new Node(5,new Node(6,new Node(10,new Node(13)))));
        return head;
    }
}

private static Node mergeNodes(Node l1, Node l2) {
        if (l1 == null ){
            return l2;
        }
        if (l2 == null) {
            return l1;
        }
        // 链表头
        Node head ;
        // 新链表添加的当前位置
        Node next ;
        // 先选出一个2个链表开头的最小值
        head = next = l1.value > l2.value ? l2:l1;
        // 头指针向后移动
        l1 = head == l1 ? l1.next : l1;
        l2 = head == l2 ? l2.next : l2;

        // 遍遍历2个链表
        while (l1 !=null && l2 != null) {
            // 遍历链表的最大值
            Node maxNode = null;
            // 链表1值大
            if(l1.value <= l2.value) {
                maxNode = l1;
                l1 = l1.next;
            } else {
                // 链表2值大
                maxNode = l2;
                l2 = l2.next;
            }
            // 添加到新链表 next向后移
            next.next = maxNode;
            next = next.next;
        }

        // 判断哪个链表还没有遍历完 直接加到新链表末尾
        next.next = l1 == null ? l2 :l1;
        // 返回head
        return head;
    }

private static Node mergeNodesRec(Node l1, Node l2) {
        // 如果l1 链表已经遍历完了
        if (l1 == null) {
            return l2;
        }
        // 如果l2 链表已经遍历完了
        if (l2 == null) {
            return l1;
        }

        Node head ;

        if(l1.value <= l2.value) {
            head = l1;
            l1 = l1.next;
        } else {
            head = l2;
            l2 = l2.next;
        }
        // 递归调用 设置next
        head.next = mergeNodesRec(l1,l2);
        return head;
    }