C# – Tips for String

public static string ReverseWord(string strInput)
{
   StringBuilder resultStr = new StringBuilder();
   int startI = strInput.Length - 1;
   for (int i = startI; i >= 0; i--)
   {
      resultStr.Append(strInput[i]);
   }

   return resultStr.ToString();
}


static void Main(string[] args)
{
  string strInput = "Damiano Abballe";
  Console.WriteLine(strInput);
  Console.WriteLine(ReverseWord(strInput));
}

public static string ReverseString(string strInput)
{
   StringBuilder resultStr = new StringBuilder();
   var arrayInput = strInput.Split(' ');
   int startI = arrayInput.Length - 1;
   for (int i = startI; i >= 0; i--)
   {
      resultStr.Append($"{arrayInput[i]} ");
   }

   return resultStr.ToString().Trim();
}


static void Main(string[] args)
{
   string strInput = "Welcome to my blog";
   Console.WriteLine(strInput);
   Console.WriteLine(ReverseString(strInput));
}

public static void CountCharacters(string strInput)
{
   // With a Regular Expressions, we will remove all space
   strInput = Regex.Replace(strInput.ToUpper(), @"\s+", "");
   var countChar = new Dictionary<char, int>();
   int endI = strInput.Length - 1;
   int oldCount = 1;

   for (int i = 0; i <= endI; i++)
   {
      if (countChar.ContainsKey(strInput[i]))
      {
         oldCount = countChar[strInput[i]];
         countChar[strInput[i]] = oldCount + 1;
      }
      else
      {
         countChar.Add(strInput[i], 1);
      }
    }

    // Display the Counter
    for (int i = 0; i < countChar.Count; i++)
    {
       Console.WriteLine($"Character: {countChar.ElementAt(i).Key},  Count: {countChar.ElementAt(i).Value}");
    }
}


static void Main(string[] args)
{
   string strInput = "hello world";
   CountCharacters(strInput);
}

public static void FindSubstring(string strInput)
{
   int currentStart = 0;
   int endI = strInput.Length - 1;
   int endSubstring = 1;
   StringBuilder result = new StringBuilder();

   while (currentStart <= strInput.Length - 1)
   {
      for (int i = currentStart; i <= endI; i++)
      {
         result.Append($"{strInput.Substring(currentStart, endSubstring)},");
         endSubstring++;
      }
      endSubstring = 1;
      currentStart++;
   }

   Console.WriteLine(result.ToString());
}


static void Main(string[] args)
{
   string strInput = "abcd";
   Console.WriteLine(strInput);
   FindSubstring(strInput);
}

public static void RemoveDuplicareCharacters(string inputString)
{
   StringBuilder result = new StringBuilder();
   HashSet<char> noDuplicate = new HashSet<char>();
   foreach (char item in inputString)
   {
      if (noDuplicate.Add(item))
      {
         result.Append(item);
      }
   }

   Console.WriteLine(result.ToString());
}


static void Main(string[] args)
{
   string inputStr = "Coffee";
   Console.WriteLine(inputStr);
   RemoveDuplicareCharacters(inputStr);
}