> For the complete documentation index, see [llms.txt](https://mayanktyagi3111.gitbook.io/interview-prep/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mayanktyagi3111.gitbook.io/interview-prep/trees/balanced-binary-tree.md).

# Balanced Binary Tree

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.

**Example 1:**

Given the following tree `[3,9,20,null,null,15,7]`:

```
    3
   / \
  9  20
    /  \
   15   7
```

Return true.\
\
**Example 2:**

Given the following tree `[1,2,2,3,3,null,null,4,4]`:

```
       1
      / \
     2   2
    / \
   3   3
  / \
 4   4
```

Return false.

```java
class Solution {
    public int height(TreeNode root) {
        if (root == null)
            return 0;
        int leftHeight = height(root.left);
        if (leftHeight == -1)
            return -1;
        int rightHeight = height(root.right);
        if (rightHeight == -1)
            return -1;
        if (Math.abs(leftHeight - rightHeight) > 1)
            return -1;
        return Math.max(leftHeight, rightHeight) + 1;
    }

    public boolean isBalanced(TreeNode root) {
        return height(root) == -1 ? false : true;
    }
}
```