Regex to check non-repetition of a set of characters

Question

Suppose I have the set of characters [ABC]. I\'m looking for a regex that would match any permutation of the superset except the empty set, i.e.

Answer 1

This is not something that regular expressions are good at. You might just want to create a list of permutations instead, and then produce all unique substrings.

something like:

def matches(s, characters):
    if len(s) != len(set(s)):
        return False # not unique sequence of characters
    return set(s).issubsetof(set(characters))

Answer 2

OK, I must say that I've thought about your question a lot and - since you seem to be wanting something really universal and customiseable (to support as many elements as possible, etc) - this is what I think would make the most optimal solution.

What you want, from a math perspective, is to identify all permutations of a set of elements without repetition.

---

Step 1 :

Find all permutations of the set, with repetition (and store them let's say in an array)

[ABC]([ABC]{1,2})?

Sidenote : let's say you have a set with n elements, all you have to do is :

[elements]([elements]{1,n-1})?

---

Step 2 :

Filter all permutations with duplicate elements

Example code in PHP :

<?php

    function strToArray($str)
    {
        $i = 0;

        while (isset($str[$i]))
        {
            $result[$i] = $str[$i];
            $i++;
        }

        return $result;
    }

    function noDuplicates($str)
    {
        if (array_unique(strToArray($str))==strToArray($str)) return true;
        else return false;
    }

    $AAA = "AAA";
    $ABC = "ABC";

    if (noDuplicates($AAA)) echo "$AAA : ok"; else echo "$AAA : not ok\n";
    if (noDuplicates($ABC)) echo "$ABC : ok"; else echo "$ABC : not ok\n";

?>

Output :

AAA : not ok
ABC : ok