# 1973. Count Nodes Equal to Sum of Descendants

<https://leetcode.com/problems/count-nodes-equal-to-sum-of-descendants>

## Description

Given the `root` of a binary tree, return *the number of nodes where the value of the node is equal to the **sum** of the values of its descendants*.

A **descendant** of a node `x` is any node that is on the path from node `x` to some leaf node. The sum is considered to be `0` if the node has no descendants.

**Example 1:**

![](https://assets.leetcode.com/uploads/2021/08/17/screenshot-2021-08-17-at-17-16-50-diagram-drawio-diagrams-net.png)

```
**Input:** root = [10,3,4,2,1]
**Output:** 2
**Explanation:**
For the node with value 10: The sum of its descendants is 3+4+2+1 = 10.
For the node with value 3: The sum of its descendants is 2+1 = 3.
```

**Example 2:**

![](https://assets.leetcode.com/uploads/2021/08/17/screenshot-2021-08-17-at-17-25-21-diagram-drawio-diagrams-net.png)

```
**Input:** root = [2,3,null,2,null]
**Output:** 0
**Explanation:**
No node has a value that is equal to the sum of its descendants.
```

**Example 3:**

![](https://assets.leetcode.com/uploads/2021/08/17/screenshot-2021-08-17-at-17-23-53-diagram-drawio-diagrams-net.png)

```
**Input:** root = [0]
**Output:** 1
For the node with value 0: The sum of its descendants is 0 since it has no descendants.
```

**Constraints:**

* The number of nodes in the tree is in the range `[1, 105]`.
* `0 <= Node.val <= 105`

## ac

```java
```