convertBSTtoGreaterTree.py

class Solution(object):
    def convertBST(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        self.val=0
        
        def traverse(root):
            if root:
                traverse(root.right)
                root.val+=self.val
                self.val=root.val
                traverse(root.left)
        traverse(root)
        return root