LeetCode 538. Convert BST to Greater Tree

考点	难度
DFS	Medium

题目

Given the root of a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus the sum of all keys greater than the original key in BST.

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As a reminder, a binary search tree is a tree that satisfies these constraints:

The left subtree of a node contains only nodes with keys less than the node’s key.
The right subtree of a node contains only nodes with keys greater than the node’s key.
Both the left and right subtrees must also be binary search trees.

思路

inverse traversal

答案

class Solution(object):
    def convertBST(self, root):
        self.val = 0
        def visit(root):
            if root:
                visit(root.right)
                root.val += self.val
                self.val = root.val
                visit(root.left)
        visit(root)
        return root

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