[LeetCode]21. Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new
list should be made by splicing together the nodes of the first two
lists.

Example:

Input: 1->2->4, 1->3->4 Output: 1->1->2->3->4->4

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
    ListNode trueHead=new ListNode(0);
    ListNode cur=trueHead;
    while(l1!=null || l2!=null){
        if(l1==null){
            cur.next=l2;
            l2=l2.next;
        }else if(l2==null){
            cur.next=l1;
            l1=l1.next;
        }else if(l1.val<=l2.val){
            cur.next=l1;
            l1=l1.next;
        }else{
            cur.next=l2;
            l2=l2.next;
        }
        cur=cur.next;
    }   
    return trueHead.next;    
}