正则表达式中的可选字符 [英] Optional characters in a regex
问题描述
任务非常简单，但是我还无法提出一个好的解决方案:字符串可以包含数字，破折号和加号，或者只能包含数字.
The task is pretty simple, but I've not been able to come up with a good solution yet: a string can contain numbers, dashes and pluses, or only numbers.
^[0-9+-]+$
满足我的大部分需求，除非用户输入"+-+-+"之类的垃圾
does most of what I need, except when a user enters garbage like "+-+--+"
我还没有经常走前路的运气，因为破折号和加号可能位于字符串中的任何地方.
I've not had luck with regular lookahead, since the dashes and pluses could potentially be anywhere in the string.
有效字符串:
- 234654
- 24-3 + -2
- -234
- 25485 +
无效:
- ++-+
推荐答案
怎么样:
^[0-9+-]*[0-9][0-9+-]*$
这确保字符串中的某处至少有一个数字. (虽然看起来可能有很多回溯.但是，另一方面，它没有在另一个+或*内包裹+或*，我也不喜欢.)
This ensures that there is at least one digit somewhere in the string. (It looks like it might have a lot of backtracking, though. But on the other hand it doesn't have a + or * wrapped inside another + or *, which I don't like either.)
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