LeetCode - 2 - Add Two Numbers

 class Solution {

    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode result = new ListNode();
        boolean carry = false;
        ListNode pointerL1 = l1, pointerL2 = l2,
             resultPointer = result;
        while (pointerL1 != null && pointerL2 != null) {
            int sum = pointerL1.val + pointerL2.val;
            if (carry) {
                sum += 1;
                carry = false;
            }
            if (sum >= 10) {
                carry = true;
                sum = sum % 10;
            }
            resultPointer.val = sum;
            pointerL1 = pointerL1.next;
            pointerL2 = pointerL2.next;
            if (pointerL1 != null || pointerL2 != null || carry) {
                resultPointer.next = new ListNode();
            }
            resultPointer = resultPointer.next;
        }   
            
         while (pointerL1 != null) {
            int sum = pointerL1.val;
            if (carry) {
                sum += 1;
                carry = false;
            }
            if (sum >= 10) {
                carry = true;
                sum = sum % 10;
            }
            resultPointer.val = sum;
            pointerL1 = pointerL1.next;
            if (pointerL1 != null || carry) {
                resultPointer.next = new ListNode();
            }
            resultPointer = resultPointer.next;
        }    
        
        while (pointerL2 != null) {
            int sum = pointerL2.val;
            if (carry) {
                sum += 1;
                carry = false;
            }
            if (sum >= 10) {
                carry = true;
                sum = sum % 10;
            }
            resultPointer.val = sum;
            pointerL2 = pointerL2.next;
            if (pointerL2 != null || carry) {
                resultPointer.next = new ListNode();
            }
            resultPointer = resultPointer.next;
        }
        
        if (carry) {
            resultPointer.val = 1;
        }
        
        return result;
    }
}