Python | Leetcode Python题解之第538题把二叉搜索树转换为累加树

题目：

题解：

class Solution:
    def convertBST(self, root: TreeNode) -> TreeNode:
        def getSuccessor(node: TreeNode) -> TreeNode:
            succ = node.right
            while succ.left and succ.left != node:
                succ = succ.left
            return succ
        
        total = 0
        node = root

        while node:
            if not node.right:
                total += node.val
                node.val = total
                node = node.left
            else:
                succ = getSuccessor(node)
                if not succ.left:
                    succ.left = node
                    node = node.right
                else:
                    succ.left = None
                    total += node.val
                    node.val = total
                    node = node.left

        return roota