package q98

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

func isValid(node *TreeNode) (bool, int, int) {
	if node.Left == nil && node.Right == nil {
		return true, node.Val, node.Val
	}

	minv, maxv := node.Val, node.Val

	if node.Left != nil {
		valid, lmin, lmax := isValid(node.Left)
		if !valid || lmax >= node.Val {
			return false, 0, 0
		}
		minv = lmin
	}
	if node.Right != nil {
		valid, rmin, rmax := isValid(node.Right)
		if !valid || rmin <= node.Val {
			return false, 0, 0
		}
		maxv = rmax
	}

	return true, minv, maxv
}

func isValidBST(root *TreeNode) bool {
	valid, _, _ := isValid(root)
	return valid
}

var _ = isValidBST