/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func longestUnivaluePath(root *TreeNode) int {
	max := 0
	if root == nil {
		return max
	}
	helper(root, &max)
	return max - 1
}

func helper(root *TreeNode, max *int) int {
	l, r := 0, 0
	if root.Left != nil {
		l = helper(root.Left, max)
		if root.Left.Val != root.Val {
			l = 0
		}
	}
	if root.Right != nil {
		r = helper(root.Right, max)
		if root.Right.Val != root.Val {
			r = 0
		}
	}
	if *max < 1+l+r {
		*max = 1 + l + r
	}
	return 1 + maxInt(l, r) // !!important
}

func maxInt(x, y int) int {
	if x < y {
		return y
	}
	return x
}