Check Whether All Binary-Tree Nodes Carry One Value
Company: Amazon
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
Return true if every node of the binary tree rooted at `root` has the same value, and false otherwise.
```cpp
class Solution {
public:
bool isUnivalTree(TreeNode* root);
};
```
### Examples
**Example 1:**
```text
Input: root = [7,7,null,7]
Output: true
Explanation: All three existing nodes have value7.
```
**Example 2:**
```text
Input: root = [4,4,4,null,5]
Output: false
Explanation: The node with value5 differs from the root value4.
```
### Constraints
- The tree contains1 to100 nodes.
- `0 <= Node.val < 100`.
### Contract considerations
The original input is a TreeNode pointer; level-order examples describe shape only.
```hint Read the boundary condition
One fixed reference value is enough to check every node.
```
### Boundary reminders
The original input is a TreeNode pointer; level-order examples describe shape only.
Overview: Check Whether All Binary-Tree Nodes Carry One Value. Return true if every node of the binary tree rooted at root has the same value, and false otherwise.
