Given a binary tree, you need to compute the length of the diameter of the tree. 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.

**Example:**

Given a binary tree

Return **3**, which is the length of the path [4,2,1,3] or [5,2,1,3].

**Note:** The length of path between two nodes is represented by the number of edges between them.

```
/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
var maxV int;
func diameterOfBinaryTree(root *TreeNode) int {
maxV = 0
travel(root)
return maxV;
}
func travel(root *TreeNode) int {
if root == nil {
return 0
}
left := travel(root.Left);
right := travel(root.Right);
maxV = max(maxV, left + right)
return max(left, right) + 1
}
func max(a, b int) int {
if a > b {
return a
}
return b
}
```