Simple Tree

class Node<T>
{
    public T Value { get; set; }

    public List<Node<T>> children { get; set; }

    public bool HasParent { get; set; }

    public Node()
    {
        this.children = new List<Node<T>>();
    }

    public Node(T value)
        : this()
    {
        this.Value = value;
    }
}

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        int N = int.Parse(Console.ReadLine());

        Node<int>[] nodes = new Node<int>[N];

        for (int i = 0; i <= N; i++)
        {
            string edgeAsString = Console.ReadLine();
            string[] edgeParts = edgeAsString.Split(' ');

            int parent = int.Parse(edgeParts[0]);
            nodes[parent].Value = parent;
            int child = int.Parse(edgeParts[1]);
            nodes[parent].children.Add(new Node<int>(child));
            nodes[child].Value = child;
            nodes[child].HasParent = true;
        }
    }

    public Node<int> FindRoot(Node<int>[] nodes)
    {
        foreach (var node in nodes)
        {
            foreach (var child in node.children)
            {
                if (child.HasParent == false)
                {
                    return child;
                }
            }
        }

        return null;
    }

    public List<Node<int>> FindAllLeafs(Node<int>[] nodes)
    {
        List<Node<int>> result = new List<Node<int>>();
        foreach (var node in nodes)
        {
            if (node.children == null)
            {
                result.Add(node);
            }
        }

        return result;
    }

    public List<Node<int>> FindMidleNodes(Node<int>[] nodes)
    {
        List<Node<int>> result = new List<Node<int>>();
        foreach (var node in nodes)
        {
            if (node.children.Count > 0 && node.HasParent == true)
            {
                result.Add(node);
            }
        }

        return result;
    }

    public int FindLongestPath(Node<int> root)
    {
        if (root.children.Count == 0)
        {
            return 0;
        }

        int maxPath = 0;
        foreach (var node in root.children)
        {
            maxPath = Math.Max(maxPath, FindLongestPath(node));
        }

        return maxPath + 1;
    }
}