A string contains at least one but no more than 2 letters "n" in C# regular expression?

Question

Given a string, how could I write a regular expression that matches when the string contains at least one but no more than 2 letters "n" at any position? So far, I only came up with n{1,2}

http://regexstorm.net/tester

And why does it need to be a regular expression? An extension method `bool ContainsMoreThanAndLessThan(this string s, char c, int minOcurrences, int maxOccurences)` is trivial and much more flexible. — InBetween, Jan 26 '16 at 17:46

Toto · Accepted Answer · 2016-01-26T17:48:12.943

3

I'd use:

 ^[^n]*n[^n]*n?[^n]*$

Where [^n]* stands for 0 or more NON n

It will match at least one n and at most 2 n

According to comment, you could use:

^(?:[^n]*n[^n]*){1,2}$

You can change {1,2} into {3,5} or anything you want.

edited Jan 26 '16 at 17:48

answered Jan 26 '16 at 17:32

Toto

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Thank you for your answer. It works, but is there a better way to do it? The ideal solution I wish to have is that by simply changing two numbers in the regex, i would be able to change the occurrences. – An Overflowed Stack Jan 26 '16 at 17:43
What does NON stands? – katie lu Jan 02 '18 at 09:44
@katielu: Not the letter "n". – Toto Jan 02 '18 at 09:56

vks · Answer 2 · 2016-01-26T17:41:30.257

1

^(?!(?:.*n){3}).*n.*$

You can add a lookahead for the same.See demo.

https://regex101.com/r/cZ0sD2/10

or

^(?!(?:[^\nn]*n){3}).*n.*$

https://regex101.com/r/cZ0sD2/11

edited Jan 26 '16 at 17:41

answered Jan 26 '16 at 17:33

vks

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@AnOverflowedStack here you can change `3` to anything u want – vks Jan 26 '16 at 17:51

score 0 · Answer 3 · answered Jan 26 '16 at 17:55

Why use Regex at all? This is trival to implement in an extension method that is highly mantainable and flexible.

public static bool ContainsMoreThanAndLessThan(this string s, char c, int maxOcurrences, int minOcurrences)
{
    Debug.Assert(maxOcurrences >= minOcurrences);
    Debug.Assert(minOcurrences > 0);
    Debug.Assert(s != null);

    if (s.Length < minOcurrences)
    {
        return false;
    }

    var ocurrences = 0;

    foreach (var ch in s)
    {
        if (ch == c)
        {
            ocurrences++;
        }

        if (ocurrences > maxOcurrences)
        {
            return false;
        }
    }

    return ocurrences >= minOcurrences;
}

Because this is a practice assignment on regular expression. :( — An Overflowed Stack, Jan 26 '16 at 17:57

score 0 · Answer 4 · edited May 23 '17 at 11:59

0

Another example Regex, adapted from this answer, will give you a match on 1 or two occurrences of the character.

"^([^n]*n){1,2}[^n]*$"

Is there a reason this cannot be solved with a simple method as InBetween suggests?

edited May 23 '17 at 11:59

Community

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answered Jan 26 '16 at 18:01

TVOHM

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A string contains at least one but no more than 2 letters "n" in C# regular expression?

4 Answers4