# 110. Balanced Binary Tree

## Easy

***

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

> a binary tree in which the left and right subtrees of _every_ node differ in height by no more than 1.

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**Example 1:**

![](https://assets.leetcode.com/uploads/2020/10/06/balance_1.jpg)

```
Input: root = [3,9,20,null,null,15,7]
Output: true
```

**Example 2:**

![](https://assets.leetcode.com/uploads/2020/10/06/balance_2.jpg)

```
Input: root = [1,2,2,3,3,null,null,4,4]
Output: false
```

**Example 3:**

```
Input: root = []
Output: true
```

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**Constraints:**

* The number of nodes in the tree is in the range `[0, 5000]`.
* `-104 <= Node.val <= 104`
