二叉树第三十三道题目二叉树转化成累加树，python版本有误

[xu2023-ICT]

其他语言版本中，python迭代版本2中，result完全没有必要

class Solution:
    def convertBST(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        if not root: return root
        stack = []
        result = []
        cur = root
        pre = 0
        while cur or stack:
            if cur:
                stack.append(cur)
                cur = cur.right
            else: 
                cur = stack.pop()
                cur.val+= pre
                pre = cur.val
                cur =cur.left
        return root

[xu2023-ICT]

class Solution:
    def convertBST(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        if not root:
            return None
        cur = root
        pre = 0
        stack = []
        # stack负责回溯，cur负责遍历 只有既没有回溯节点和遍历节点的时候，循环才会停止
        while stack or cur:
            if cur:
                stack.append(cur)
                cur = cur.right
            else:
                # 遇到空节点 回溯
                cur = stack.pop()
                cur.val += pre
                pre = cur.val
                cur = cur.left
        return root