# Largest Binary Search Subtree in Value

Given a binary tree `root`

, return the largest sum of a subtree that is also a binary search tree.

**Constraints**

`0 ≤ n ≤ 100,000`

where`n`

is the number of nodes in`root`

https://binarysearch.com/problems/Largest-Binary-Search-Subtree-in-Value

## Examples

### Example 1

**Input**

- root =

**Output**

- answer =
`9`

**Explanation**

The binary search tree rooted at `3`

has the largest sum with `3 + 2 + 4 = 9`

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