# 0538. Convert BST to Greater Tree

<https://leetcode.com/problems/convert-bst-to-greater-tree>

## Description

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 sum of all keys greater than the original key in BST.

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.

**Note:** This question is the same as 1038: <https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/>

**Example 1:**

![](https://assets.leetcode.com/uploads/2019/05/02/tree.png)

```
**Input:** root = [4,1,6,0,2,5,7,null,null,null,3,null,null,null,8]
**Output:** [30,36,21,36,35,26,15,null,null,null,33,null,null,null,8]
```

**Example 2:**

```
**Input:** root = [0,null,1]
**Output:** [1,null,1]
```

**Example 3:**

```
**Input:** root = [1,0,2]
**Output:** [3,3,2]
```

**Example 4:**

```
**Input:** root = [3,2,4,1]
**Output:** [7,9,4,10]
```

**Constraints:**

* The number of nodes in the tree is in the range `[0, 104]`.
* `-104 <= Node.val <= 104`
* All the values in the tree are **unique**.
* `root` is guaranteed to be a valid binary search tree.

## ac

```java
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int sum = 0;

    public TreeNode convertBST(TreeNode root) {
        if (root == null) return root;
        convertBST(root.right);
        sum += root.val;
        root.val = sum;
        convertBST(root.left);
        return root;
    }
}

/*
1) get total sum; 2) in-order traversal, total sum - prev sum;
update from right to left, add each node.val to sum, update node.val = sum
*/
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://jaywin.gitbook.io/leetcode/solutions/0538-convert-bst-to-greater-tree.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.