using System;

​

namespace ConsoleApp1

{

    public delegate string ReverseDelegate(string input);

    public class Program

    {

        public static void Main()

        {

            var input = "Hello World!";

            // --------------//

            // 1. 字串反轉    //

            // --------------//

            Console.WriteLine($"[Normal Method] Reversed string:{ReverseString(input)}");

​

            // --------------------------------------//

            // 2. 透過Extension Methods來達成字串反轉 //

            // -------------------------------------//

​

            //Console.WriteLine($"[Extension Method] Reversed string:{input.Reverse()}");

​

            // ---------------------

            // 3. Delegate

            // Note 1 => CustomStringHelper allow you to pass in customized reverse function.

            // Note 2 => Please implement remove all spaces before reverse for CustomStringHelper.Reverse

            // Expected Result: !dlroWolleH

            // ---------------------

            // 這裡可以最多三行補程式

            //

            //

            //

            //var helper = new CustomStringHelper(?);

            //Console.WriteLine($"[Delegate] Reversed string:{helper.Reverse(input)}");

        }

        public static string ReverseString(string text)

        {

            int i = 0;

            int j = text.Length-1;

            var array = text.ToCharArray();

            while (i<j)

            {

                var temp = array[i];

                array[i] = array[j];

                array[j] = temp;

                i++;

                j--;

            }

            return new string(array);

        }

    }

​

    public static class StringExtension

    {

        //TODO

    }

​

    public class CustomStringHelper

    {

        public CustomStringHelper(ReverseDelegate reverseDelegate)

        {

            _reverseDelegate = reverseDelegate;

        }

​

        private readonly ReverseDelegate _reverseDelegate;

        public string Reverse(string input)

        {

           return _reverseDelegate(input);

        }

    }

}

​