Leetcode: Merging 2 sorted lists
Style wise, the assignment currRes = currRes.next; happens no matter what, so lift it out of if-else clause:

            if (l1.val &lt; l2.val)
            {
                currRes.next = l1;
                l1 = l1.next;
            }
            else
            {
                currRes.next = l2;
                l2 = l2.next;
            }    
            currRes = currRes.next;


Correctness wise, the condition if (l1.val &lt; l2.val) loses the stability: if the elements compare equal, the one from l2 is merged first. Consider if (l1.val &lt;= l2.val) (or even if (l2.val &lt; l2.val)) instead. It is not required by the problem statement, and it doesn't matter for ints. In real life however the stability is of utmost importance, and as an interviewer I'd definitely mark it.

On the bright side, a dummy head for the merged list is a right way to go.