message: Update maximum-difference-between-node-and-ancestor.py
diff: @@ -18,7 +18,7 @@ class Solution(object):
  """
  result = 0
  stack = [(root, 0, float("inf"))]
  - while len(stack) > 0:
  + while stack:
  node, mx, mn = stack.pop()
  if not node:
  continue
  