# Most Frequent Subtree Sum

Given a binary tree `root`

, find the most frequent subtree sum. The subtree sum of a node is the sum of all values under a node, including the node itself. You can assume there is one unique solution.

**Constraints**

`n ≤ 100,000`

where`n`

is the number of nodes in`root`

https://binarysearch.com/problems/Most-Frequent-Subtree-Sum

## Examples

### Example 1

**Input**

- root =

**Output**

- answer =
`2`

**Explanation**

`2`

occurs twice: once as the left leaf, and once as the sum of `2 + 5 - 5`

.

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