message: update difference on versions
  minor change
diff: @@ -32,7 +32,7 @@ class Solution(object):
  if l2:
  val += l2.val
  l2 = l2.next
  - carry, val = val / 10, val % 10
  + carry, val = val / 10, val % 10 # val = val//10 if python 3
  current.next = ListNode(val)
  current = current.next
  