using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        // Every line bellow should output True

        // Happy Numbers

        Console.WriteLine(IsHappyNumber(1));

        Console.WriteLine(IsHappyNumber(7));

        Console.WriteLine(IsHappyNumber(10));

        Console.WriteLine(IsHappyNumber(97));

        Console.WriteLine(IsHappyNumber(100));

        Console.WriteLine(IsHappyNumber(130));

​

        // Sad Numbers

        Console.WriteLine(!IsHappyNumber(2));

        Console.WriteLine(!IsHappyNumber(3));

        Console.WriteLine(!IsHappyNumber(4));

        Console.WriteLine(!IsHappyNumber(5));

        Console.WriteLine(!IsHappyNumber(6));

        Console.WriteLine(!IsHappyNumber(8));

        Console.WriteLine(!IsHappyNumber(9));

    }

    public static bool IsHappyNumber(int number)

    {

        bool isNumberEqualsOne = number == 1;

        bool isNumberASingleDigitHappyNumber = number == 7;

        if (isNumberEqualsOne || isNumberASingleDigitHappyNumber)

            return true;

        bool isNumberASingleDigitSadNumber = number < 10 && number != 1 && number != 7;

        if (isNumberASingleDigitSadNumber)

            return false;

​

        return IsHappyNumber(GetSumOfTheSquareOfDigits(number));

    }

​

    public static int GetSumOfTheSquareOfDigits(int number)

    {

        var individualDigits = number.ToString().Select(digit => Char.GetNumericValue(digit));

        return (int)individualDigits.Select(digit => Math.Pow(digit, 2)).Sum();

    }

}