# Only Child

Given a binary tree `root`

, return the number of nodes that are an only child. A node `x`

is an only child if its parent has exactly one child (`x`

).

**Constraints**

`n ≤ 100,000`

where`n`

is the number of nodes in`root`

https://binarysearch.com/problems/Only-Child

## Examples

### Example 1

**Input**

- root =

**Output**

- answer =
`2`

**Explanation**

Node `1`

is an only child and `3`

is an only child.

### Example 2

**Input**

- root =

**Output**

- answer =
`1`

**Explanation**

Node `3`

is an only child

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