using System;

using System.Diagnostics;

using System.Text; 

using System.Text.RegularExpressions; 

​

​

public static class StringExtensions {

        public static string GetAllIntRegex(this string numint)

        {

          return Regex.Replace(numint, "[^0-9]", "");

        }

​

        public static string GetLeadIntFast(this string numint)

        {

            bool minus = false; //we pass in absolute number

            if (numint.IndexOf('-') == 0)

            {

                minus = true;

                numint = numint.Replace("-", ""); //we expect this to be in first place, not bullet proof but GE

            }

            else if (numint.IndexOf('+') == 0)

                numint = numint.Replace("+", "");

​

            char[] n = numint.ToCharArray();

            StringBuilder sb = new StringBuilder(); 

            for (int i = 0; i < n.Length; i++)

            {

                if (!char.IsDigit(n[i]))

                    break; 

​

                sb.Append(n[i]); 

            }

​

            if (minus)

                return string.Concat("-", sb.ToString());

            return sb.ToString();

        }

​

        public static string GetLeadIntFaster(this string numint)

        {

            bool minus = false; //we pass in absolute number

            if (numint.IndexOf('-') == 0)

            {

                minus = true;

                numint = numint.Replace("-", ""); //we expect this to be in first place

            }

            else if (numint.IndexOf('+') == 0)

                numint = numint.Replace("+", "");

​

​

            char[] n = numint.ToCharArray();

            int exit = 0;

            for (int i = 0; i < n.Length; i++)

            {

                if (!char.IsDigit(n[i])) {

                    exit = i; 

                    break;

                }

            }

            Array.Resize(ref n, exit);

​

            if (minus)

                return string.Concat("-", new string(n));

            return new string(n); 

        }

​

        public static string GetLeadIntFastest(this string numint)

        {

            bool minus = false; //we pass in absolute number

            if (numint.IndexOf('-') == 0)

            {

                minus = true;

                numint = numint.Substring(1); //we expect this to be in first place

            }

            else if (numint.IndexOf('+') == 0)

                numint = numint.Substring(1);

​

​

            char[] n = numint.ToCharArray();

            int exit = 0;

            for (int i = 0; i < n.Length; i++)

            {

                if (!char.IsDigit(n[i]))

                {

                    exit = i;

                    break;

                }

            }

            Array.Resize(ref n, exit);

​

            if (minus)

                return string.Concat("-",  new string(n));

​

            return new string(n); 

        }

​

        public static int TryParser(this string numint)

        {

            int y = 0;

            //This is a fair comparison, we must get digits only

            Int32.TryParse(numint.GetLeadIntFast(), out y); //this alone is fast at 502 ticks

            return y;

​

        }

​

        public static int TryParserFaster(this string numint)

        {

            int y = 0;

            //This is a fair comparison, we must get digits only

            Int32.TryParse(numint.GetLeadIntFaster(), out y); //this alone is fast at 502 ticks

            return y;

​

        }

​

        public static int TryParserFastest(this string numint)

        {

            int y = 0;

            //This is a fair comparison, we must get digits only

            Int32.TryParse(numint.GetLeadIntFastest(), out y); //this alone is fast at 502 ticks

            return y;

​

        }

​

        public static int TryParserRegex(this string numint)

        {

            int y = 0;

            //This is a fair comparison, we must get digits only

            Int32.TryParse(numint.GetAllIntRegex(), out y); //this alone is fast at 502 ticks

            return y;

​

​

        }

        /// <summary>

        /// Fastest wat to convert a numeric string into an int

        /// </summary>

        /// <param name="numint">must be numbers and signs only</param>

        /// <returns></returns>

        public static int StartsWithInt(this string numint)

        {

            bool minus = false; //we pass in absolute number

            if (numint.IndexOf('-') == 0)

            {

                minus = true;

                numint = numint.Replace("-", ""); //we expect this to be in first place, not bullet proof but GE

            }

            else if (numint.IndexOf('+') == 0)

                numint = numint.Replace("+", "");

​

            int total = 0; //must be zero

            for (int i = 0; i < numint.Length; i++)

            {

                if (numint[i] >= '0' && numint[i] <= '9')  //get lead number only

                {

                    if (total * 10 + (numint[i] - '0') < 0) //we get into negative, if over int.MaxValue

                        return int.MaxValue; //return what you want or throw error

​

                    total = total * 10 + (numint[i] - '0');

                }

                else

                    break;

                //return int.MinValue;

​

            }

​

            if (minus) total *= -1;

            return total;

​

        }

​

        /// <summary>

        /// Fastest way to convert lead digits in a string into an int

        /// </summary>

        /// <param name="intStr">must be numbers and signs only</param>

        /// <returns></returns>

        public static int StartsWithIntFaster(this string intStr)

        {

            bool minus = false; //we pass in absolute number

            if (intStr.IndexOf('-') == 0)

            {

                minus = true;

                intStr = intStr.Replace("-", ""); //we expect this to be in first place, not bullet proof but GE

            }

            else if (intStr.IndexOf('+') == 0)

                intStr = intStr.Replace("+", "");

​

            int sum = 0; //must be zero

            char[] n = intStr.ToCharArray();

            for (int i = 0; i < n.Length; i++)

            {

                if (n[i] >= 48 && n[i] <= 57)  //'0'=48 and '9'=57 get lead number only

                {

                    int z = sum * 10 + (n[i] - 48);  

                    if (z < 0) //we get into negative, if over int.MaxValue

                        return int.MaxValue; //return what you want or throw error

                    sum = z;

                }

                else

                    break;

                //return int.MinValue;

​

            }

​

            if (minus) sum *= -1;

            return sum;

​

        }

​

​

        /// <summary>

        /// Fastest way to convert lead digits in a string into an int

        /// </summary>

        /// <param name="intStr">must be numbers and signs only</param>

        /// <returns></returns>

        public static int StartsWithIntFastest(this string intStr)

        {

            bool minus = false; //we pass in absolute number

            if (intStr.IndexOf('-') == 0)

            {

                minus = true;

                intStr = intStr.Substring(1); //we expect this to be in first place, not bullet proof but GE

            }

            else if (intStr.IndexOf('+') == 0)

                intStr = intStr.Substring(1);

​

            int sum = 0; //must be zero start

            char[] n = intStr.ToCharArray();

​

            for (int i = 0; i < n.Length; i++)

            {

                if (n[i] >= 48 && n[i] <= 57)  //'0'=48 and '9'=57 get lead number only

                {

                    int z = sum * 10 + (n[i] - 48);

                    if (z < 0) //we get into negative, if over int.MaxValue

                        return int.MaxValue; //return what you want or throw error

                    sum = z;

                }

                else

                    break;

                    //return int.MinValue; //or throw error

​

            }

​

            if (minus) sum *= -1;

            return sum;

​

        }

​

}

​

public class Program

{

    public static void Main()

    {

            Stopwatch sw = new Stopwatch();

            sw.Start();

            Console.WriteLine("12451a 1"); 

            Console.WriteLine("12451a 1".StartsWithInt());

            sw.Stop();

            Console.WriteLine(sw.ElapsedTicks.ToString() + " ticks");

            sw.Reset();

            sw.Start();

            Console.WriteLine("12452a 2");

            Console.WriteLine("12452a 2".StartsWithIntFaster());

            sw.Stop();

            Console.WriteLine(sw.ElapsedTicks.ToString() + " ticks");

            sw.Reset();

            sw.Start();

            Console.WriteLine("Winner - 12453a 3");

            Console.WriteLine("12453a 3".StartsWithIntFastest());

            sw.Stop();

            Console.WriteLine(sw.ElapsedTicks.ToString() + " ticks");

            sw.Reset();

            sw.Start();

            Console.WriteLine("12454a 4");

            Console.WriteLine("12454a 4".TryParser());

            sw.Stop();

            Console.WriteLine(sw.ElapsedTicks.ToString() + " ticks");

            sw.Reset();

            sw.Start();

            Console.WriteLine("12455a 5");

            Console.WriteLine("12455a 5".TryParserFaster());

            sw.Stop();

            Console.WriteLine(sw.ElapsedTicks.ToString() + " ticks");

            sw.Reset();

            sw.Start();

            Console.WriteLine("12456a 6");

            Console.WriteLine("12456a 6".TryParserFastest());

            sw.Stop();

            Console.WriteLine(sw.ElapsedTicks.ToString() + " ticks");

            sw.Reset();

            sw.Start();

            Console.WriteLine("This grabs all numbers and NOT LEAD digits - 12457a 7");

            Console.WriteLine("12457a 7".TryParserRegex());

            sw.Stop();

            Console.WriteLine(sw.ElapsedTicks.ToString() + " ticks");

        Console.WriteLine("0".StartsWithIntFastest());

        Console.WriteLine("10".StartsWithIntFastest());

        Console.WriteLine("-12345".StartsWithIntFastest());

        Console.WriteLine("1234".StartsWithIntFastest());

        Console.WriteLine("123".StartsWithIntFastest());

        Console.WriteLine("+12346".StartsWithIntFastest());

        Console.WriteLine("-1234".StartsWithIntFastest());

        Console.WriteLine("21474813649".StartsWithIntFastest()); 

    }

}