using System;

​

​

public class GFG 

{ 

​

// Function to return the string after 

// reversing the alternate k characters 

​

static String revAlternateK(String s, 

​

                            int k, int len) 

{ 

​

    for (int i = 2; i < s.Length;) 

​

    { 

​

​

        // If there are less than k characters 

​

        // starting from the current position 

​

        if (i + k > len) 

​

            break; 

​

​

        // Reverse first k characters 

​

        s = s.Substring(0, i) +  

​

            reverse(s.Substring(i, k).ToCharArray(), 0, k - 1) + 

​

            s.Substring(i + k); 

​

​

        // Skip the next k characters 

​

        i += 2 * k; 

​

    } 

​

    return s; 

} 

​

static String reverse(char []str, int start, int end)  

{ 

​

​

    // Temporary variable to store character  

​

    char temp; 

​

    while (start <= end) 

​

    { 

​

        // Swapping the first and last character  

​

        temp = str[start]; 

​

        str[start] = str[end]; 

​

        str[end] = temp; 

​

        start++; 

​

        end--; 

​

    } 

​

    return String.Join("", str); 

}  

​

// Driver code 

​

public static void Main(String[] args)  

{ 

​

    String s = "abcdefghijk"; 

​

    int len = s.Length; 

​

    int k = 2; 

​

    Console.WriteLine(revAlternateK(s, k, len)); 

} 

} 

​

​

​

​