convert-bst-to-greater-tree.py

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


class Solution:
    def convertBST(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        self.sum = 0

        def dfs(node):
            if not node:
                return 0
            dfs(node.right)
            self.sum += node.val
            node.val = self.sum
            dfs(node.left)

        dfs(root)
        return root