1038. Binary Search Tree to Greater Sum Tree (Medium) - TengnanYao/daily_leetcode GitHub Wiki

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def bstToGst(self, root: TreeNode) -> TreeNode:
        self.sum = 0
        def dfs(root):
            if root:
                dfs(root.right)
                root.val = self.sum = self.sum + root.val
                dfs(root.left)
            return root
        return dfs(root)