C# Online Compiler | .NET Fiddle

using System;using System.Text; using System.Diagnostics; using System.Linq; 

public static class Program
{
	public static string RemoveWhiteSpace(this string s)
	{
		char[] r = new char[s.Length]; 
		int idxr = 0; 
		for (int i = 0; i < s.Length; i++) {
			if ( !Char.IsWhiteSpace(s[i])) {
				r[idxr] = s[i];
				idxr++;
			}
		}
		return new string(r); 
	}
	
	public static string StringBuilderRemoveWhiteSpace(this string s) {
		
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < s.Length; i++) {
			if ( !Char.IsWhiteSpace(s[i])) {
				sb.Append(s[i]);
			}
    
		}
		return sb.ToString(); 
	}
	
	public static string LinqRemoveWhiteSpace(this string s) {
	
		return new string(s.ToCharArray().Where(c => !Char.IsWhiteSpace(c)).ToArray());
		
	}	
	
	//public static string NormalizeWhiteSpaceForLoop(this string input)
    public static string FastRemoveWhiteSpace(this string input)
    {
        int len = input.Length,
            index = 0,
            i = 0;
        var src = input.ToCharArray();
        //bool skip = false;
        char ch;
        for (; i < len; i++)
        {
            ch = src[i];
            switch (ch)
            {
                case '\u0020':
                case '\u00A0':
                case '\u1680':
                case '\u2000':
                case '\u2001':
                case '\u2002':
                case '\u2003':
                case '\u2004':
                case '\u2005':
                case '\u2006':
                case '\u2007':
                case '\u2008':
                case '\u2009':
                case '\u200A':
                case '\u202F':
                case '\u205F':
                case '\u3000':
                case '\u2028':
                case '\u2029':
                case '\u0009':
                case '\u000A':
                case '\u000B':
                case '\u000C':
                case '\u000D':
                case '\u0085':
                    //if (skip) continue;
                    //src[index++] = ch;
                    //skip = true;
                    continue;
                default:
                    //skip = false;
                    src[index++] = ch;
                continue;
            }
        }

        return new string(src, 0, index);
    }
	
	
	public static void Main()
	{
		Stopwatch sw = new Stopwatch(); 
		string test = "China lashes out at Hong Kong protest targeting its office Mon 22-Jul-19 10:33am"; 
		sw.Start();
		Console.WriteLine(test.RemoveWhiteSpace());
		sw.Stop(); 
		Console.WriteLine(sw.ElapsedTicks.ToString()+" ticks.");
		sw.Restart();
		Console.WriteLine(test.StringBuilderRemoveWhiteSpace());
		sw.Stop(); 
		Console.WriteLine(sw.ElapsedTicks.ToString()+" ticks.");
		sw.Restart();
		Console.WriteLine(test.LinqRemoveWhiteSpace());
		sw.Stop(); 
		Console.WriteLine(sw.ElapsedTicks.ToString()+" ticks.");
		sw.Restart();
		Console.WriteLine(test.FastRemoveWhiteSpace());
		sw.Stop(); 
		Console.WriteLine(sw.ElapsedTicks.ToString()+" ticks.");
		
	}
}

        string test = "China lashes out at Hong Kong protest targeting its office Mon 22-Jul-19 10:33am"; 
 
using System;using System.Text; using System.Diagnostics; using System.Linq; 
​
public static class Program
{
    public static string RemoveWhiteSpace(this string s)
    {
        char[] r = new char[s.Length]; 
        int idxr = 0; 
        for (int i = 0; i < s.Length; i++) {
            if ( !Char.IsWhiteSpace(s[i])) {
                r[idxr] = s[i];
                idxr++;
            }
        }
        return new string(r); 
    }
    
    public static string StringBuilderRemoveWhiteSpace(this string s) {
        
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < s.Length; i++) {
            if ( !Char.IsWhiteSpace(s[i])) {
                sb.Append(s[i]);
            }