using System.Text.RegularExpressions;
public static void Main()
var regex = new Regex(@"^[a-zA-Z0-9#@][a-zA-Z0-9#@\-\.]{1,149}$"); var start = new string[]{"1", "a", "#", "@", }; var andThen = new string[]{"1", "a", "#", "@", "-", "."}; const int testLength = 151;
for (var i = 0; i < numTests; ++i)
var builder = new StringBuilder(s);
for (var j = 1; j < testLength; ++j)
var r = rand.Next() % andThen.Length;
builder.Append(andThen[r]);
var test = builder.ToString();
var isMatch = regex.IsMatch(test);
Console.WriteLine($"{test} {isMatch}");
