using System;

using System.Collections.Generic;

public class stringOccurence{

    public void Main(){

        int x;  

        string str = "ElanooBoommer";

        List<string> s = new List<String>(){""};

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

            x=0;

            for(int j = 0 ; j < str.Length; j++){

                if(str[i]==str[j]){

                    x++;

                }

            }

            //Console.WriteLine(str[i]+" = "+ x);

            if(!s.Contains(str[i].ToString()) || x<2){              

                Console.WriteLine(str[i]+" = "+ x);

                s.Add(str[i].ToString());

            }

        }

    }

​

}