using System;

using System.Collections.Generic;

class Node

{

    public int data;

    public Node left;

    public Node right;

    public Node(int val)

    {

        data = val;

        left = null;

        right = null;

    }

}

​

public class BinaryTree

{   

    void inorder(Node root)

    {

        if(root == null)

            return;

        inorder(root.left);

        Console.Write($"{root.data} ");

        inorder(root.right);

    }

    public static void Main()

    {

        int [] parent = new int[]  {-1, 0, 0, 1, 2, 2};

        var makeNode = new Dictionary<int, Node>();

        for(int i = 0; i < 6; i++) {

            Node node = new Node(i);

            makeNode[i] = node;

        }

        Node root = null;

        for(int i = 0; i < 6; i++) {

            if(parent[i] == -1) {

                root = makeNode[i];

                continue;

            }

            Node par = makeNode[parent[i]];

            if(par.left != null) {

                par.right = makeNode[i];

            }

            else {

                par.left = makeNode[i];

            }

        }

        BinaryTree tree = new BinaryTree();

        tree.inorder(root);

    }

}