Test Height Balance throughout a Binary Tree
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
Determine whether a binary tree is height-balanced. At every node, the heights of its left and right subtrees must differ by at most one. Height counts nodes on the longest downward path; an empty subtree has height 0.
```cpp
bool isBalanced(TreeNode* root);
```
Use the supplied `TreeNode` with `val`, `left`, and `right`. Example brackets describe tree structure in level order.
### Examples
```text
Input: root = [8,4,12,2,6,null,14]
Output: true
```
```text
Input: root = [8,4,12,2,null,10,null,1,null,9]
Output: false
```
In the second tree the root's two subtree heights agree, but each child subtree has an internal imbalance.
### Constraints
- The tree contains between 0 and 5000 nodes.
- Values lie between -10000 and 10000, inclusive.
- An empty tree is balanced.
Overview: Check height balance throughout a binary tree with one postorder height-and-failure computation.