LeetCode #2 - Add Two Numbers\nYou are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contains a single digit. Add the two numbers and return it as a linked list.\n\n### Input/Output\n\n**Input:**\n(2 -> 4 -> 3) + (5 -> 6 -> 4)\n\n**Output:**\n(7 -> 0 -> 8)\n\n### Constraints\n- The number of nodes in each linked list is in the range [1, 100].\n- 0 <= Node.val <= 9.\n- It is guaranteed that the list represents a valid number.

``` class ListNode { int val; ListNode next; ListNode(int x) { val = x; } }\npublic ListNode addTwoNumbers(ListNode l1, ListNode l2) {\n ListNode dummyHead = new ListNode(0);\n ListNode p = l1, q = l2, current = dummyHead;\n int carry = 0;\n while (p != null || q != null) {\n int x = (p != null) ? p.val : 0;\n int y = (q != null) ? q.val : 0;\n int sum = carry + x + y;\n carry = sum / 10;\n current.next = new ListNode(sum % 10);\n current = current.next;\n if (p != null) p = p.next;\n if (q != null) q = q.next;\n }\n if (carry > 0) {\n current.next = new ListNode(carry);\n }\n return dummyHead.next;\n} ```