var max int = 0

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func diameterOfBinaryTree(root *TreeNode) int {
	max = 0
	postorder(root, &max)
	return
}

func postorder(root *TreeNode, max *int) int {
	if root == nil {
		return -1
	}
	l := postorder(root.Left, max) + 1
	r := postorder(root.Right, max) + 1
	if *max < l+r {
		*max = l + r
	}
	if l < r {
		return r
	}
	return l
}