using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Text.RegularExpressions;

using System.Threading.Tasks;

​

namespace ex

{

    class Program

    {

​

        public static string Changing(string input,string key,(string,string)[]patterns)

        {

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

            {

                input = input.Replace(patterns[i].Item1, patterns[i].Item1 + key);

            }

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

            {

                input = input.Replace(patterns[i].Item1+key, patterns[i].Item2);

            }

            return input;

        }

        static void Main(string[] args)

        {

            string example = "AAABBCCCCDDEQWJJKAYZ";

            string example2 = "A/A/A/BB/CCCC//DD/"; //=>DD/DD/DD/C/VVV//ABC//

            string key = "myKey";// Value ••for conditional understanding

            (string, string)[] patterns = new (string, string)[] {("A","DD"),("BB","C"),("DD","ABC"),("CCCC","VVV")};

            Console.WriteLine(Changing(example,key,patterns));

            Console.WriteLine(Changing(example2,key,patterns));

            Console.ReadKey();

        }

    }

}

//replacements:

//A => DD

//BB => C

//DD => ABC

//CCCC => VVV

​

//output:

//DDDDDDCVVVABCEQWJJKDDYZ