using System;

using System.Collections.Generic;

using System.Linq;

​

public class Friend

{

    public string Email { get; private set; }

​

    public ICollection<Friend> Friends { get; private set; }

​

    public Friend(string email)

    {

        this.Email = email;

        this.Friends = new List<Friend>();

    }

​

    public void AddFriendship(Friend friend)

    {

        this.Friends.Add(friend);

        friend.Friends.Add(this);

    }

​

    HashSet<string> friends = new HashSet<string>();

​

    private bool CanBeConnected(Friend f, Friend s)

    {

        if (friends.Contains(f.Email)) return false;

        friends.Add(f.Email);

        return f.Email == s.Email

            || f.Friends.Any(x => CanBeConnected(x, s));

    }

​

    public bool CanBeConnected(Friend friend)

    {

        friends = new HashSet<string>();

        return CanBeConnected(this, friend);

    }

}

public class Program

{

    public static void Main()

    {

        Friend a = new Friend("A");

        Friend b = new Friend("B");

        Friend c = new Friend("C");

​

        a.AddFriendship(b);

        b.AddFriendship(c);

​

        Console.WriteLine(a.CanBeConnected(c));

    }

}