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:

**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:

**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:

**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

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