regex101: Match the longest repeating subsequence of a digit

Group 1(\d)

\da digit

Negative Lookbehind(?<!(?=\1)..)

Positive Lookahead(?=\1)

\1the text saved by group 1

.any character (except for line terminators)

Positive Lookahead(?=(\1*)(?!\1).*(?!\1).\1\2(?!\1))

Group 2(\1*)

\1*the text saved by group 1, repeated any number of times

Negative Lookahead(?!\1)

\1the text saved by group 1

.*any character (except for line terminators), repeated any number of times

Negative Lookahead(?!\1)

\1the text saved by group 1

.any character (except for line terminators)

\1the text saved by group 1

\2the text saved by group 2

Negative Lookahead(?!\1)

\1the text saved by group 1

Negative Lookahead(?!(?:(?=\2((\3?+)(\d)(\5*)))){1,592}?(?=\2\3.*(?!\5).\5\6(?!\5))(?:\1(?=\1*\4\5(\7?+\5)))*+(?!\1))

Non-Capturing Group(?:(?=\2((\3?+)(\d)(\5*)))){1,592}?

{1,592}?repeats the group contents below between 1 and 592 times:

Positive Lookahead(?=\2((\3?+)(\d)(\5*)))

\2the text saved by group 2

Group 3((\3?+)(\d)(\5*))

Group 4(\3?+)

\3?+optionally matches the text saved by group 3

Group 5(\d)

\da digit

Group 6(\5*)

\5*the text saved by group 5, repeated any number of times

Positive Lookahead(?=\2\3.*(?!\5).\5\6(?!\5))

\2the text saved by group 2

\3the text saved by group 3

.*any character (except for line terminators), repeated any number of times

Negative Lookahead(?!\5)

\5the text saved by group 5

.any character (except for line terminators)

\5the text saved by group 5

\6the text saved by group 6

Negative Lookahead(?!\5)

\5the text saved by group 5

Non-Capturing Group(?:\1(?=\1*\4\5(\7?+\5)))*+

*+repeats the group contents below any number of times:

\1the text saved by group 1

Positive Lookahead(?=\1*\4\5(\7?+\5))

\1*the text saved by group 1, repeated any number of times

\4the text saved by group 4

\5the text saved by group 5

Group 7(\7?+\5)

\7?+optionally matches the text saved by group 7

\5the text saved by group 5

Negative Lookahead(?!\1)

\1the text saved by group 1

\2the text saved by group 2

Global pattern flags

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

g modifier: global. Finds all matches instead of stopping after the first

25 tokens

Regular Expression

(\d)(?<!(?=\1)..)(?=(\1*)(?!\1).*(?!\1).\1\2(?!\1))(?!(?:(?=\2((\3?+)(\d)(\5*)))){1,592}?(?=\2\3.*(?!\5).\5\6(?!\5))(?:\1(?=\1*\4\5(\7?+\5)))*+(?!\1))\2

Unit Tests

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