// C# Extension Method

// Doc: https://csharp-extension.com/en/method/1002132/string-replacefirst

​

// @nuget: Z.ExtensionMethods

​

using System;

​

public class Program

{

    public static void Main()

    {

        string input = "aaabbbbccccaaadddddjjjjaaa";

​

        // C# Extension Method: String - ReplaceFirst

        string newStr = input.ReplaceFirst("aaa", "zzz");

        Console.WriteLine(newStr);

        // C# Extension Method: String - ReplaceFirst

        newStr = input.ReplaceFirst(2, "aaa", "zzz");

        Console.WriteLine(newStr);

    }

}