using System;

using System.Collections.Generic;

​

public class Node

{

    public int id;

    public Node left, right;

    public Node(int id)

    {

        this.id=id;

        left=right=null;

    }

}

public class Program

{

    public Node build(int[] ar)

    {

        Dictionary<int, Node> mp = new Dictionary<int, Node>();

        for(int i=0; i<ar.Length; i++)

        {

            Node tmp = new Node(i);

            mp.Add(i, tmp);

        }

        Node root = new Node(0);

        for(int i=0;i<ar.Length;i++)

        {

            if(ar[i]==-1)

                root = mp[i];

            else

            {

                Node par = mp[ar[i]];

                if(par.left==null)

                    par.left = mp[i];

                else

                    par.right = mp[i];

            }   

        }

        return root;    

    }

    void inOrder(Node root)

    {

        if(root==null)return;

        inOrder(root.left);

        Console.Write(root.id+" "); 

        inOrder(root.right);

    }

    public static void Main()

    {

        int[] ar = new int[]{-1, 0, 0, 1, 1, 3, 5};

        Program tree = new Program();

        Node root = tree.build(ar);

        tree.inOrder(root);

    }

}