Leetcode 4 – Add Two Numbers

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
  ListNode head = null;
  ListNode cur = null;
  int carry = 0;

  while(l1 != null || l2 != null){

    int value1 = l1 != null ? l1.val : 0;
    int value2 = l2 != null ? l2.val : 0;

    // both non-null
    int val = value1 + value2 + carry;
    int mod = val % 10;
    carry = val / 10;

    ListNode newValue = new ListNode(mod);

    if(head == null){
      head = newValue;
      cur = head;
    }
    else cur.next = newValue;

    cur = newValue;

    l1 = l1 != null ? l1.next : null;
    l2 = l2 != null ? l2.next : null;
  }

  if(carry != 0){
    ListNode c = new ListNode(carry);
    cur.next = c;
  }

  return head;
}