a very common use case for regexes is to find matches that are preceded or followed by some context. a classical example being all lines that end with ‘a’. this requirement is usually expressed with a lookahead, where upon finding an ‘a’, you look ahead to check if it’s the end of the line. in a backtracking engine, this is very easy to implement - you just duct-tape the logic that checks the next character, but in a DFA-based engine, this is impossible because you cannot report “the match is here” if the next character is not even known yet. and by the time you know the next character, the position information is lost, so you can’t report the match retroactively (well, unless the distance is fixed of course..).
Credit: The Pokémon Company。关于这个话题，体育直播提供了深入分析
跟“老虎”比起来，“金鱼”Dora只算得上幼雏，甚至还带着学生妹的清纯和天真。进夜总会前，她在一家发廊里当洗头妹，赚钱不多，又很辛苦，师父就把她介绍给了Maggie姐。为了盖住原先假小子模样的板寸头，上班时，她还要专门戴一顶成熟的假发。，详情可参考体育直播
command line arguments, g is an intermediate function