using System;

​

namespace Neighbors

{

    public class Program

    {

        public static void Main(string[] args)

        {

            var tree = new Neighbors();

            tree.InitRoot();

            tree.CreateNeighbors();

            tree.ShowNeighbors();

        }

​

        public class Neighbors

        {

            private Node _Root;

​

            public class Node

            {

                public Node Left;

                public Node Right;

                public Node Neighbor;

                public int Value;

​

                public Node(int value)

                {

                    this.Value = value;

                }

            }

            public void CreateNeighbors()

            {

                CreateNeighbors(_Root);

            }

​

            public void ShowNeighbors()

            {

                ShowNeighbors(_Root);

            }

​

            public Node InitRoot()

            {

                _Root = new Node(8)

                {

                    Left = new Node(3)

                    {

                        Left = new Node(1),

                        Right = new Node(6)

                        {

                            Left = new Node(4),

                            Right = new Node(7)

                        }

                    },

                    Right = new Node(10)

                    {

                        Right = new Node(14)

                        {

                            Left = new Node(13)

                        }

                    }

                };

​

                return _Root;

            }

​

​

            private void CreateNeighbors(Node root)

            {

                if (root == null)

                {

                    return;

                }

​

                if (root.Left != null)

                {

                    if (root.Right != null)

                    {

                        root.Left.Neighbor = root.Right;

                    }

                    else

                    {

                        var parentNeighbor = root.Neighbor;

                        while (parentNeighbor != null)

                        {

                            var neighborNode = parentNeighbor.Left ?? parentNeighbor.Right;

                            if (neighborNode != null)

                            {

                                root.Left.Neighbor = neighborNode;

                                break;

                            }

​

                            parentNeighbor = parentNeighbor.Neighbor;

                        }

                    }

                }

​

                if (root.Right != null)

                {

                    var parentNeighbor = root.Neighbor;

​

                    while (parentNeighbor != null)

                    {

                        var neighborNode = parentNeighbor.Left ?? parentNeighbor.Right;

                        if (neighborNode != null)

                        {

                            root.Right.Neighbor = neighborNode;

                            break;

                        }

​

                        parentNeighbor = parentNeighbor.Neighbor;

                    }

                }

​

                CreateNeighbors(root.Right);

                CreateNeighbors(root.Left);

            }

​

            private void ShowNeighbors(Node root)

            {

                var currentNode = root;

                while (currentNode != null)

                {

                    var node = currentNode;

                    currentNode = null;

​

                    while (node != null)

                    {

                        if (currentNode == null)

                        {

                            currentNode = node.Left ?? node.Right;

                        }

​

                        Console.Write(node.Value + " ");

                        node = node.Neighbor;

                    }

                    Console.WriteLine();

                }

            }

        }

    }

}