package main

type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

func main() {

}

func diameterOfBinaryTree(root *TreeNode) int {
	a, b := maxpath(root.Right)
	c, d := maxpath(root.Left)
	return max(a+b, c, d)
}

func maxpath(p *TreeNode) (int, int) {
	if p == nil {
		return 0, 0
	}
	leftpathnum, leftcurmax := maxpath(p.Left)
	rightpathnum, rightcurmax := maxpath(p.Right)
	curmax := max(leftpathnum+rightpathnum, leftcurmax, rightcurmax)

	return 1 + max(leftpathnum+rightpathnum), curmax
}