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
}