using System;

public class Program

{

    public static void Main()

    {

        string word1 = "abc11223cabbbb321";

        countDuplicateChar(word1);

        string word2 = "abc11223cabbbb321ddfffeee";

        countDuplicateChar(word2);

    }

    static void countDuplicateChar(string word)

    {

        // convert string to char array

        char[]S = word.ToCharArray();

        // get length of string

        int n = S.Length;

        // string has 1 character then return it

        if (n < 2)

        {

            return;

        }

​

        //to compare with previous character

        int j = 0;

        //number of duplicates

        int duplicate = 0;

        // to hold last duplicate character

        char? lastChar = null;

​

        // loop throught the charcter of string

        for (int i = 1; i < n; i++)

        {

            lastChar = lastChar ?? S[j];

            // if character is same and last character is not like current then squesce is over

            if (S[j] == S[i] && lastChar != S[i])

            {

                lastChar = S[i];

                duplicate += 1;

            }

            // if last and current character is not same increase the last character index by 1

            else if (S[j] != S[i])

            {

                j++;

                S[j] = S[i];

            }

        }

        char[] A = new char[j + 1];

        //copy the part of array from S to A with the size of j+1

        Array.Copy(S, 0, A, 0, j + 1);

        string response = string.Format("Duplicates in {0} = {1}", word, duplicate);

        Console.WriteLine(response);

    }

}