using System.Linq; 

using System.Diagnostics;

using System;

using System.Text;

using System.Globalization; 

public static class Program

{

    public static string UnicodeReplaceAt(this string str, int offset, char replaceChar)

    {

        int count=1; 

        string replaceBy = replaceChar.ToString(); 

        return new StringInfo(str).ReplaceByPosition(replaceBy, offset, count).String;

    }

​

    public static StringInfo ReplaceByPosition(this StringInfo str, string replaceBy, int offset, int count)

    {

        return str.RemoveByTextElements(offset, count).InsertByTextElements(offset, replaceBy);

    }

​

    public static StringInfo RemoveByTextElements(this StringInfo str, int offset, int count)

    {

        return new StringInfo(string.Concat(

            str.SubstringByTextElements(0, offset),

            offset + count < str.LengthInTextElements

                ? str.SubstringByTextElements(offset + count, str.LengthInTextElements - count - offset)

                : ""

            ));

    }

    public static StringInfo InsertByTextElements(this StringInfo str, int offset, string insertStr)

    {

        if (string.IsNullOrEmpty(str.String))

            return new StringInfo(insertStr);

        return new StringInfo(string.Concat(

            str.SubstringByTextElements(0, offset),

            insertStr,

            str.LengthInTextElements - offset > 0 ? str.SubstringByTextElements(offset, str.LengthInTextElements - offset) : ""

        ));

    }   

   public static string SubsituteStringStringBuilder(this string s, int idx, char replaceChar)

   {

       if (string.IsNullOrEmpty(s) || idx >= s.Length || idx < 0) 

                    return s; 

       return new StringBuilder(s).Remove(idx, 1).Insert(idx, replaceChar.ToString()).ToString();

   }

​

    public static string ReplaceAtSubstring(this string s, int idx, char replaceChar)

    {

        if (string.IsNullOrEmpty(s) || idx >= s.Length || idx < 0) 

                    return s; 

        return s.Substring(0,idx) + replaceChar.ToString() + s.Substring(idx+replaceChar.ToString().Length,s.Length - (idx+replaceChar.ToString().Length) );

    }

    public static string ReplaceAtStringManipulation(this string s, int idx, char replaceChar)

    {

        if (string.IsNullOrEmpty(s) || idx >= s.Length || idx < 0) 

                    return s; 

         return s.Remove(idx, 1).Insert(idx, replaceChar.ToString());

    }

    public static string ReplaceAtLinq(this string value, int index, char newchar)

    {

        if (value.Length <= index)

            return value;

        else

            return string.Concat(value.Select((c, i) => i == index ? newchar : c));

    }

​

    public static string ReplaceAtCharArray(this string input, uint index, char newChar)

    {

        if (string.IsNullOrEmpty(input) || index >= input.Length) 

            return input;

​

        char[] chars = input.ToCharArray();

        chars[index] = newChar;

        return new string(chars);

    }

​

    public static void Main()

    {

        Stopwatch sw = new Stopwatch();

        sw.Start();

        Console.WriteLine("ReplaceAtCharArraySSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSƾƾƾƾ".ReplaceAtCharArray(70,'X')); 

        sw.Stop();

        Console.WriteLine("in {0} ticks.",sw.ElapsedTicks.ToString("N0")); 

        sw.Restart();

        Console.WriteLine("ReplaceAtLinqSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSƾƾƾƾ".ReplaceAtLinq(70,'Y')); 

        sw.Stop();

        Console.WriteLine("in {0} ticks.",sw.ElapsedTicks.ToString("N0")); 

        sw.Restart();

        Console.WriteLine("ReplaceAtStringManipulationSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSƾƾƾƾ".ReplaceAtStringManipulation(70,'Z')); 

        sw.Stop();

        Console.WriteLine("in {0} ticks.",sw.ElapsedTicks.ToString("N0")); 

        sw.Restart();

        Console.WriteLine("ReplaceAtSubstringgggggggggSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSƾƾƾƾ".ReplaceAtSubstring(70,'R')); 

        sw.Stop();

        Console.WriteLine("in {0} ticks.",sw.ElapsedTicks.ToString("N0")); 

​

        sw.Restart();

        Console.WriteLine("SubsituteStringStringBuilderSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSƾƾƾƾ".SubsituteStringStringBuilder(70,'Ɯ')); 

        sw.Stop();

        Console.WriteLine("in {0} ticks.",sw.ElapsedTicks.ToString("N0")); 

​

        sw.Restart();

        Console.WriteLine("UnicodeReplaceAtSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSƾƾƾƾ".UnicodeReplaceAt(50,'Ɯ')); 

        sw.Stop();

        Console.WriteLine("in {0} ticks.",sw.ElapsedTicks.ToString("N0")); 

​

    }

}