using System;

using static System.Console;

using System.Diagnostics;

using  System.Text.RegularExpressions;

using System.Linq;

using System.Text;

​

public class Program {

    public static void Main() {

        const int total = 1_000_000;

        var cpf = "111.222.333-44";

        var formatado = "";

        var sw = Stopwatch.StartNew();

        for (var i = 0; i < total; i++) {

            formatado = cpf.Substring(0, 3) + cpf.Substring(4, 3) + cpf.Substring(8, 3) + cpf.Substring(12, 2);

        }

        sw.Stop();

        WriteLine(sw.ElapsedMilliseconds);

        sw.Restart();

        for (var i = 0; i < total; i++) {

            formatado = string.Concat(cpf.AsSpan(0, 3), cpf.AsSpan(4, 3), cpf.AsSpan(8, 3), cpf.AsSpan(12, 2));

        }

        sw.Stop();

        WriteLine(sw.ElapsedMilliseconds);

        sw.Restart();

        for (var i = 0; i < total; i++) {

            formatado = cpf[0..3] + cpf[4..7] + cpf[8..11] + cpf[12..14];

        }

        sw.Stop();

        WriteLine(sw.ElapsedMilliseconds);

        sw.Restart();

        for (var i = 0; i < total; i++) {

            var sb = new StringBuilder(cpf.Length);

            foreach (var letra in cpf) if (Char.IsDigit(letra)) sb.Append(letra);

            formatado = sb.ToString();

        }

        sw.Stop();

        WriteLine(sw.ElapsedMilliseconds);

        sw.Restart();

        for (var i = 0; i < total; i++) {

            formatado = string.Join("", cpf.ToCharArray().Where(Char.IsDigit));

        }

        sw.Stop();

        WriteLine(sw.ElapsedMilliseconds);

        sw.Restart();

        for (var i = 0; i < total; i++) {

            formatado = String.Join("", Regex.Split(cpf, @"[^\d]"));

        }

        sw.Stop();

        WriteLine(sw.ElapsedMilliseconds);

        sw.Restart();

        for (var i = 0; i < total; i++) {

            Regex r = new Regex(@"\d+");            

            var result = "";

            foreach (Match m in r.Matches(cpf)) result += m.Value;

            formatado = result;

        }

        sw.Stop();

        WriteLine(sw.ElapsedMilliseconds);

    }

}