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.

MergeTwoSortedLists.java

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