Grindr XTRAOptions: One week ($14.99), One month ($22.99), Three months ($49.99), One year ($149.99)
The rational test case
。爱思助手下载最新版本对此有专业解读
For additional guidance:
you can match a string by repeatedly taking derivatives for each character. when you’ve consumed the entire input, you check if the resulting regex accepts the empty string (is “nullable”). if yes, the original string matched.