using System;

using System.Diagnostics;

​

public static class StringExtensions {

        /// <summary>

        /// Fastest way to to find 1st number in a string and convert it into an integer

        /// </summary>

        /// <param name="intStr"></param>

        /// <returns></returns>

        //https://metadataconsulting.blogspot.com/2020/06/CSharp-Fastest-way-to-find-a-number-or-integer-in-a-string.html

        public static int GetFirstIntFast(this string intStr)

        {

            int sum = 0; //must be zero

            char[] n = intStr.ToCharArray(); //fastest way to index a string

            int idxFirstDigit = -1;  

​

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

            {

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

                {

                    if (idxFirstDigit == -1) idxFirstDigit = i; 

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

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

                        return int.MaxValue; //or throw error

                    sum = z;

                }

                else if (idxFirstDigit>-1)

                    break;

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

            }

​

            if (intStr.IndexOf('-') == idxFirstDigit-1) //chek for neg sign

                sum *= -1;

            return sum;

​

        }

        public static int GetFirstIntFaster(this string n)

        {

            int sum = 0; //must be zero

            int idxFirstDigit = -1;  

​

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

            {

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

                {

                    if (idxFirstDigit == -1) idxFirstDigit = i; 

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

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

                        return int.MaxValue; //or throw error

                    sum = z;

                }

                else if (idxFirstDigit>-1)

                    break;

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

            }

​

            if (n.IndexOf('-') == idxFirstDigit-1) //chek for neg sign

                sum *= -1;

            return sum;

​

        }

}

​

public class Program

{

    public static void Main()

    {

            int a = 0; 

            int b = 0; 

            Stopwatch sw = new Stopwatch();

            sw.Start();

            a = "aaaa12451a 1".GetFirstIntFast();

            sw.Stop();

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

            sw.Reset();    

            sw.Start();

            b = "aaaa12451a 1".GetFirstIntFaster();

            sw.Stop();

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

            sw.Reset();

            sw.Start();

            a = "aaaaa-12452a 2".GetFirstIntFast();

            sw.Stop();

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

            sw.Reset();    

            sw.Start();

            b = "aaaaa-12452a 2".GetFirstIntFaster();

            sw.Stop();

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

            sw.Reset();

            sw.Start();

            a = "aaaaaaccccccccccccccccccccccccccccccccc+12453a 3".GetFirstIntFast();

            sw.Stop();

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

            sw.Reset();    

            sw.Start();

            b = "aaaaaaccccccccccccccccccccccccccccccccc+12453a 3".GetFirstIntFaster();

            sw.Stop();

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

            sw.Reset();

            sw.Start();

            a = "aaaaaaaaaaaaaaaaa 4".GetFirstIntFast();

            sw.Stop();

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

            sw.Reset();    

            sw.Start();

            b = "aaaaaaaaaaaaaaaaa 4".GetFirstIntFaster();

            sw.Stop();

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

            sw.Reset();

            sw.Start();

            a = "1122222222222222222222 5".GetFirstIntFast();

            sw.Stop();

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

            sw.Reset();    

            sw.Start();

            b = "1122222222222222222222 5".GetFirstIntFaster();

            sw.Stop();

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

            sw.Reset();

    }

}