MOSTest

using System;
using System.Diagnostics;
using System.Text;
using System.Threading.Tasks;

namespace MOSTest
{
    class MainClass
    {
        /// <summary>
        /// Random number generator. Only used to generate a test password.
        /// </summary>
        public static Random Random = new Random();

        /// <summary>
        /// Password to ifnd
        /// </summary>
        public static string Password;

        /// <summary>
        /// Legal password characters
        /// </summary>
        public static string LegalCharacters =
            "abcdefghijklmnopqrstuvwxyz" +
            "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
            "0123456789" +
            "~`!@#$%^&*()_+-=";

        /// <summary>
        /// Test driver
        /// </summary>
        /// <param name="args"></param>
        public static void Main(string[] args)
        {
            // Generate a test password
            Password = GenerateRandomPassword(4);
            Console.WriteLine("Passowrd is " + Password);

            // Find the password using the Task Parallel Library.
            var stopwatch = Stopwatch.StartNew();
            var word = ParallelTestAllWords("");
            stopwatch.Stop();
            if (word != null) Console.WriteLine("Parallel: Answer is " + word + "; Elapsed = " + stopwatch.Elapsed);
            else Console.WriteLine("Parallel: No answer found");

            // Find the password using a sequential foreach
            stopwatch = Stopwatch.StartNew();
            word = SequentialTestAllWords("");
            stopwatch.Stop();
            if (word != null) Console.WriteLine("Sequential: Answer is " + word + "; Elapsed = " + stopwatch.Elapsed);
            else Console.WriteLine("Sequential: No answer found");
        }

        /// <summary>
        /// Generate a random password for testing
        /// </summary>
        /// <param name="length">Length of the password</param>
        /// <returns>Test password</returns>
        private static string GenerateRandomPassword(int length)
        {
            var buf = new StringBuilder(length);
            for (var i = 0; i < length; i++)
            {
                buf.Append(LegalCharacters[Random.Next(LegalCharacters.Length)]);
            }
            return buf.ToString();
        }

        /// <summary>
        /// Use the TPL to find the password
        /// </summary>
        /// <param name="guess">Current guess</param>
        /// <returns>The password that was found, or null if not found</returns>
        private static string ParallelTestAllWords(string guess)
        {
            // If the guess is the correct length, see if it is the correct password
            if (guess.Length == Password.Length)
            {
                // If it is the correct password, return it
                if (string.Equals(guess, Password)) return guess;

                // Otherwise indicate not found by returning null
                return null;
            }

            // The guess isn't long enough. Try all the words beginning
            // with the guess.
            string result = null;
            Parallel.ForEach(LegalCharacters, (ch, state) =>
            {
                // Check the guess extended with one of the legal characters
                var word = ParallelTestAllWords(guess + ch);

                // If this is the password, return it and stop the loop
                if (word != null)
                {
                    result = word;
                    state.Break();
                }
            });

            // Return the password if found or null if not found
            return result;
        }

        /// <summary>
        /// Use a foreach loop to find the password
        /// </summary>
        /// <param name="guess">Current guess</param>
        /// <returns>The password that was found, or null if not found</returns>
        private static string SequentialTestAllWords(string guess)
        {
            // If the guess is the correct length, see if it is the correct password
            if (guess.Length == Password.Length)
            {
                // If it is the correct password, return it
                if (string.Equals(guess, Password)) return guess;

                // Otherwise indicate not found by returning null
                return null;
            }

            // The guess isn't long enough. Try all the words beginning
            // with the guess.
            foreach (var ch in LegalCharacters)
            {
                // Check the guess extended with one of the legal characters
                var word = SequentialTestAllWords(guess + ch);

                // If this is the password, return it and stop the loop
                if (word != null) return word;
            }

            // Password not found.
            return null;
        }
    }
}