comefrom: <doocs>0563.Binary Tree Tilt_1.py
code: def sum(root):
      if root is None:
          return 0
      nonlocal ans
      left = sum(root.left)
      right = sum(root.right)
      ans += abs(left - right)
      return root.val + left + right
masked: def sample_funcname ( var_1 ) :
      if var_1 is None :
          return 0
      nonlocal var_4
      left = var_0 ( var_1.left )
      right = var_0 ( var_1.right )
      var_4 += abs ( left - right )
      return var_1.val + left + right
  