Problem 2 Add Two Numbers

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode ans = new ListNode(0);
        ListNode head = ans;
        int c = 0;
        while(l1!=null || l2!=null || c > 0){
            int sum = c;
            if(l1!=null){
                sum += l1.val;
                l1 = l1.next;
            }
            if(l2!=null){
                sum += l2.val;
                l2 = l2.next;
            }
            c = sum / 10;
            sum %= 10;
            ListNode newNode = new ListNode(sum);
            head.next = newNode;
            head = head.next;
        }
        return ans.next;
    }
}