problem 4 - bulls and cows

using System;

class Program
{
    static void Main()
    {
        string secret = Console.ReadLine();
        int bulls = int.Parse(Console.ReadLine());
        int cows = int.Parse(Console.ReadLine());
        int answers = 0;
        for (int i1 = 1; i1 <= 9; i1++)
        {
            for (int i2 = 1; i2 <= 9; i2++)
            {
                for (int i3 = 1; i3 <= 9; i3++)
                {
                    for (int i4 = 1; i4 <= 9; i4++)
                    {
                        int guess = i1 * 1000 + i2 * 100 + i3 * 10 + i4;
                        string guessStr = guess.ToString();
                        int guessBulls = 0;
                        int guessCows = 0;
                        for (int digit = 0; digit < 4; digit++)
                        {
                            char currentSecret = secret[digit];
                            bool isBull = false;
                            if (currentSecret == guessStr[digit])
                            {
                                isBull = true;
                                guessBulls += 1;
                            }
                            if (isBull)
                                continue;
                            for (int otherDigit = 0; otherDigit < 4; otherDigit++)
                            {
                                if (otherDigit == digit)
                                    continue;
                                if (currentSecret == guessStr[otherDigit] &&
                                    guessStr[otherDigit] != secret[otherDigit])
                                {
                                    guessCows += 1;
                                    break;
                                }
                            }
                        }
                        if (guessCows == cows && guessBulls == bulls)
                        {
                            Console.Write(guess + " ");
                            answers += 1;
                        }
                    }
                }
            }
        }
        if (answers == 0)
            Console.WriteLine("No");
    }
}