Add Two Numbers

2. Add Two Numbers

Solution

1. Need to keep pre and check if pre is 0 at the end. Cleaner Solution

   def addTwoNumbers(self, l1, l2):
    """
    :type l1: ListNode
    :type l2: ListNode
    :rtype: ListNode
    """
    res = ListNode(0)
    tail = res
    pre = 0
    while l1 or l2:
        val = pre
        if l1:
            val += l1.val
            l1 = l1.next
        if l2:
            val += l2.val
            l2 = l2.next
        tail.next = ListNode(val % 10)
        pre = val // 10
        tail = tail.next
    while pre != 0:
        tail.next = ListNode(pre % 10)
        pre = pre // 10
        tail = tail.next
       
    return res.next