using System;

using System.Text.RegularExpressions;

                    using System.Text;

​

public class Program

{

    public static void Main()

    {

        string text = @"hi         hiiiii

        hwwww           aaaaaaaaa

        awdw

        aaaaaaaaaa";

​

            Console.Write(RemoveExcessiveWhitespace(text));    

    }

        public static string RemoveExcessiveWhitespace(string value)

        {

            if (value == null) { return null; }

​

            value = value.Trim().Replace("\r", " ");

            value = value.Trim().Replace("\n", " ");

            value = value.Trim().Replace(Environment.NewLine, " ");

            var builder = new StringBuilder();

            var ignoreWhitespace = false;

            foreach (var c in value)

            {

                if (!ignoreWhitespace || c != ' ')

                {

                    builder.Append(c);

                }

                ignoreWhitespace = c == ' ';

            }

            return builder.ToString();

        }

}