Regular Expressions 101

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Regular Expression
.NET 7.0 (C#)

^(?:(?<Number>)(?<Prime>(?<SmallestFactor>(?<char>.)\<char>+?))(?:\<SmallestFactor>+(?<-Prime>(?=)))?(?!\<char>)(?<-char>)(?(Prime)(?<-SmallestFactor>)(?<-Number>)|(?<Composite-Number>))|(?<Unit>.)|(?<MustUseTheSameCharacter>.+))$|(?<Zero>^$)

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Description

Inspects lines that contain only a character, let's say c, repeated n times. The name of the matching groups will tell you if n is 0, the unit 1, a prime number, or a composite number.

Alternative

Removing the outermost anchors ^ and $ from the first (and very large) alternate group will do the same but, instead of inspecting per line, it will inspect any repetition of a character (line breaks, obviously, stop repetitions).

^(?: ...... )$|(?<Zero>^$)

(?: ...... )|(?<Zero>^$)

Submitted by kevinhp - a year ago