正则表达式

using System.Text;
using System.Text.RegularExpressions;   // 使用正则必须引入这个命名空间

namespace ConsoleApp1;

public class App
{
  public static void Main()
  {
    string input = "1851 1999 1950 1905 2003";
    string pattern = @"(?<=19)\d{2}\b";

    foreach (Match match in Regex.Matches(input, pattern))
      Console.WriteLine(match.Value);
  }
}