using System;

public class Program

{

    public static void Main()

    {

        //Console.WriteLine("Hello World");

        Permutation("abc", "");

    }

    private static void Permutation(string str, string prefix){

        System.Console.WriteLine($"\n\n>>> string str={str}, string prefix={prefix}<<<<\n");

        if (str.Length == 0){

            System.Console.WriteLine($"RESULT:{prefix}\n\n");

        }else{

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

                Console.WriteLine($"__ PERM __: str.Substring(0,{i}):'{str.Substring(0,i)}' + str.Substring({i} + 1)='{str.Substring(i + 1)}';");

                string perm = str.Substring(0,i) + str.Substring(i + 1);

                Console.WriteLine($"__ PERM __: {perm};");

​

                System.Console.WriteLine($"prefix='{prefix}' + str[{i}]='{str[i]}'");

                System.Console.WriteLine($"__ PREFIX __='{prefix + str[i]}'");              

                Permutation(perm, prefix + str[i]);                                      

            }

        }

    }

}