message: Update next-greater-element-iii.py
diff: -# Time: O(logn)
  -# Space: O(logn)
  +# Time: O(logn) = O(1)
  +# Space: O(logn) = O(1)
  # Given a positive 32-bit integer n, you need to find the smallest 32-bit integer
  # which has exactly the same digits existing in the integer n and is greater in value than n.
  