Given a binary tree, write a program to compute the **length of the diameter** of the tree.

**Problem Note**

- The diameter of a binary tree is the length of the
**longest**path between any two nodes in a tree. This path may or may not pass through the root. - The length of the path between two nodes is represented by the number of edges between them.

**Example**

```
Input: Given a binary tree
1
/ \
2 3
/ \
4 5
Output: 3
Explanation: Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3]
```