using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        const int min = 0;

        const int max = 999999;

        var range = Enumerable.Range(min, max + 1);

        var paddedRange = range.Select(number => number.ToString("D6")).ToList(); // D6 means pad number with leading zeros up to 6 characters length

        var totalCount = paddedRange.Count();

        var happyCount = paddedRange.Count(paddedNumber => {

            var left = paddedNumber.Substring(0, 3);

            var right = paddedNumber.Substring(3, 3);

            var sumLeft = left.Select(character => int.Parse(character.ToString())).Sum();

            var sumRight = right.Select(character => int.Parse(character.ToString())).Sum();

            return sumLeft == sumRight;

        });

​

        Console.WriteLine($"Happy: {happyCount}");

        Console.WriteLine($"Total: {totalCount}");

        Console.WriteLine($"Ratio: {(float)happyCount / totalCount}");

    }

}