using System;

public class Program

{

    public static void Main()

    {

        Node node1 = new Node(1);

        Node node2 = new Node(3);

        Node node3 = new Node(6);

        Node node4 = new Node(8);

        Node node5 = new Node(2) { Left = node1, Right = node2 };

        Node node6 = new Node(7) { Left = node3, Right = node4 };

        Node node7 = new Node(5) { Left = node5, Right = node6 };

        int[] array = new int[5] { 1, 3, 5, 6, 7 };

        Console.WriteLine(IsAllInBST3(array, node7));

    }

    public class Node

    {

        public Node Left {get; set;}

        public Node Right {get; set;}

        public int Value {get; set;}

​

        public Node(int value) { Value = value; }

        public Node FindElement(int element)

        {

            if (element == Value)

                return this;

            else if (element < Value)

                return Left?.FindElement(element);

            else

                return Right?.FindElement(element);

        }

    }

    public static bool InorderTraversal(int[] array, Node node, ref int index)

    {  

        if (node == null)

            return false;

​

        // left, center, right

        if (InorderTraversal(array, node.Left, ref index))

            return true;

​

        if (node.Value == array[index])

            ++index;

​

        if (index == array.Length)

            return true;

​

        return InorderTraversal(array, node.Right, ref index);

    }

​

​

    public static bool IsAllInBST3(int[] array, Node root)

    {

        int index = 0;

        return InorderTraversal(array, root, ref index);

    }

}