ADS

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ASD
{
    class Program
    {
        static int GCD(int a, int b)
        {
            while (b != 0)
            {
                int t = b;
                b = a % b;
                a = t;
            }
            return a;
        }

        static int GCDR(int a, int b)
        {
            if (b == 0)
            {
                return a;
            }
            return GCDR(b, a % b);
        }

        static int GCD3(int a, int b, int c)
        {
            return GCD(GCD(a, b), c);
        }

        static int GCDN(params int[] nums)
        {
            int result = nums[0];
            for (int i = 1; i < nums.Length; i++)
            {
                result = GCD(result, nums[i]);
            }
            return result;
        }

        static int DigitSumI(int num)
        {
            int sum = 0;
            while (num != 0)
            {
                sum += num % 10;
                num /= 10;
            }
            return sum;
        }

        static int DigitSum(int num)
        {
            if (num < 10)
            {
                return num;
            }
            return num % 10 + DigitSum(num / 10);
        }

        static int DigitRoot(int num)
        {
            if (num < 10)
            {
                return num;
            }
            return DigitRoot(DigitSum(num));
        }

        static int count = 0;
        static int ArrayWalk(int[] arr, int index)
        {
            if (index < 0 || index >= arr.Length || arr[index] == -1)
            {
                Console.WriteLine("out");
                return 0;
            }
            Console.Write(arr[index] + "->");
            if (DigitSum(arr[index]) % 2 == 0)
            {
                arr[index] = -1;
                return 1 + ArrayWalk(arr, index + 3);
            }
            else
            {
                arr[index] = -1;
                return 1 + ArrayWalk(arr, index - 2);
            }
        }

        static int EvenCount(int[] arr, int index)
        {
            if (index >= arr.Length)
            {
                return 0;
            }
            if (arr[index] % 2 == 0)
            {
                return 1 + EvenCount(arr, index + 1);
            }
            else
            {
                return EvenCount(arr, index + 1);
            }
        }

        static bool EGNCheck(string egn)
        {
            if (egn.Length != 10)
            {
                return false;
            }
            int[] coeff = { 2, 4, 8, 5, 10, 9, 7, 3, 6 };
            int digit = 0;
            for (int i = 0; i < 9; i++)
            {
                digit += (egn[i] - '0') * coeff[i];
            }
            digit %= 11;
            if (digit == 10)
            {
                digit = 0;
            }
            if (digit == (egn[9] - '0'))
            {
                return true;
            }
            return false;
        }

        static void Main(string[] args)
        {
            Console.WriteLine(EGNCheck("6101057509"));
            /*int[] arr = { 5, 23, 77, 123, 681, 9, 772, 16 };
            Console.WriteLine("Even count: " + EvenCount(arr, 0));
            /*int steps = ArrayWalk(arr, 4);
            Console.WriteLine(steps);*/
        }
    }
}