LC 1038 0538 [M] [M] Binary Search Tree to Greater Sum Tree, Convert BST to Greater Tree - ALawliet/algorithms GitHub Wiki

we want to calculate the suffix sum, so by the time we get to a node we have the running sum from the number greater than it

# 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:
    suffixsum = 0
    def bstToGst(self, root):
        if root.right:
            self.bstToGst(root.right)
            
        print(root.val)
        
        root.val = root.val + self.suffixsum
        self.suffixsum = root.val
        
        if root.left:
            self.bstToGst(root.left)
        
        return root
# 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:
    suffixsum = 0
    
    def convertBST(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        if not root: return None
        
        if root.right:
            self.convertBST(root.right)
            
        print(root.val)
        
        root.val = root.val + self.suffixsum
        self.suffixsum = root.val
        
        if root.left:
            self.convertBST(root.left)
        
        return root