LeetCode 合并两个有序链表

https://leetcode-cn.com/problems/merge-two-sorted-lists/description/
感觉没有头节点的链表使用起来很麻烦：

public  class ListNode {
     int val;
     ListNode next;
     ListNode(int x) { val = x; }
 }

class Solution {
    public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {
            if(l1==null)
                return l2;
            if(l2==null)
                return l1;
            ListNode l3 = new ListNode(l1.val);
            l3=l1.val<=l2.val?l1:l2;
            ListNode res =l3; 
            if(l1.val<=l2.val)l1=l1.next;
            else l2=l2.next;
            while(l1!=null&&l2!=null) {

                if(l1.val<=l2.val){

                        l3.next=l1;
                    l3=l1;
                    l1=l1.next;
                }
                else {
                        l3.next=l2;
                    l3=l2;
                    l2=l2.next;
                } 
            }
            if(l1==l2)
                return res;
            if(l1==null)
            l3.next=l2;
            else

                l3.next=l1;
            return res;
    }
    public static void main(String[] args) {
        ListNode l1= new ListNode(1);
        ListNode ll1 = l1;
        l1.next = new ListNode(2);
        l1.next = new ListNode(4);
        ListNode l2= new ListNode(1);
        ListNode ll2 = l2;
        l2.next = new ListNode(3);
        l2.next = new ListNode(4);
        mergeTwoLists(ll1,ll2);
    }
}

提交记录中，耗费时间最短的是递归算法：

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) return l2;
        if (l2 == null) return l1;

        ListNode head = null;
        if (l1.val <= l2.val){
            head = l1;
            head.next = mergeTwoLists(l1.next, l2);
        } else {
            head = l2;
            head.next = mergeTwoLists(l1.next, l2);
        }
        return head;
    }
}