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
