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# 1038. Binary Search Tree to Greater Sum Tree

<https://leetcode.com/problems/binary-search-tree-to-greater-sum-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 538: <https://leetcode.com/problems/convert-bst-to-greater-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 `[1, 100]`.
* `0 <= Node.val <= 100`
* All the values in the tree are **unique**.
* `root` is guaranteed to be a valid binary search tree.

## ac

```java
```