using System; 

public class GFG 

{ 

    private static void permute(String prefix,String str, 

                                int l, int r) 

    { 

        if (l == r) 

            Console.WriteLine(prefix+str); 

        else

        { 

            for (int i = l; i <= r; i++) 

            { 

                str = swap(str, l, i);

                prefix = swap(prefix, l, i);

                permute(prefix,str, l + 1, r); 

                str = swap(str, l, i);

                prefix = swap(prefix, l, i);

​

            } 

        } 

    } 

    public static String swap(String a,  

                              int i, int j) 

    { 

        char temp; 

        char[] charArray = a.ToCharArray(); 

        temp = charArray[i] ; 

        charArray[i] = charArray[j]; 

        charArray[j] = temp; 

        string s = new string(charArray); 

        return s; 

    } 

​

public static void Main() 

{ 

    String prefix = "abc";

    String str = "2013";

    if(prefix.Length.Equals(str.Length))

       {

            int n = str.Length;

            permute(prefix,str, 0, n-1); 

       }

       else

       {

           Console.WriteLine("Error. Strings have to be equal in length");

       }

​

} 

}