一道本来想用全局变量的题目

class Solution:
    my_sum = 0
    def convertBST(self, root: TreeNode) -> TreeNode:
        global my_sum
        if root is None: 
            return
        self.convertBST(root.right)
        print(root.val)
        
        tmp = root.val
        root.val += my_sum
        my_sum += tmp

        self.convertBST(root.left)

        return root

错误：

NameError: name ‘my_sum’ is not defined
Line 18 in convertBST (Solution.py)
Line 14 in convertBST (Solution.py)
Line 48 in _driver (Solution.py)
Line 59 in (Solution.py)

fix: 类变量一定要使用 self 来引用之

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    my_sum = 0
    def convertBST(self, root: TreeNode) -> TreeNode:
        if root is None: 
            return

        self.convertBST(root.right)
        tmp = root.val
        root.val += self.my_sum
        self.my_sum += tmp
        self.convertBST(root.left)

        return root
'''
执行用时 :
132 ms
, 在所有 Python3 提交中击败了
16.13%
的用户
内存消耗 :
15.9 MB
, 在所有 Python3 提交中击败了
5.44%
的用户
'''