using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"^(?!(?:[^A\n]*A){2})(?!(?:[^B\n]*B){3})(?!(?:[^C\n]*C){2})(?!(?:[^D\n]*D){2})(?:[ABCD](?:\s|$)){3}";
string input = @"# These are valid:
A B C
A B B
B C B
D A B
# These are invalid:
A A B
B B B";
RegexOptions options = RegexOptions.Multiline;
foreach (Match m in Regex.Matches(input, pattern, options))
{
Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
}
}
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx