正则表达式：为什么负向前瞻后的数字捕获不起作用？
(.)(?!\1)\1
我认为这应该匹配任何字符 [c]，后跟任何不是 [c] 的字符，然后再次跟 [c]。
像“aba”、“xyx”
但在线正则表达式验证器告诉我我错了。问题出在哪里？
提前致谢。
(.)(?!\1)\1
I think this should match any character [c], followed by any character that is not [c], then followed by [c] again.
like 'aba', 'xyx'
But online regexr validator is telling me im wrong. Where is the issue?
Thanks in advance.
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评论（1）
您正确地检查了第二个字符是否与第一个（组）相同，但您忘记允许第二个字符匹配。
(.)(?!\1).\1https://regex101 .com/r/vvapcB/1
如果您还希望匹配仅包含 3 个字符，则
(?=.{3}$)(.)(?!\1).\1https://regex101.com/r/2IVxNK/1
You were correctly checking if the second character isn't the same as the first (group), but you forgot to allow a match on the second character otherwise.
(.)(?!\1).\1https://regex101.com/r/vvapcB/1
If you want to also want the matches to be 3 characters only,
(?=.{3}$)(.)(?!\1).\1https://regex101.com/r/2IVxNK/1