PHP regular expression permutations

Question

I have a string e.g. HRJSHR and search for a way to find all possible permutations of A-Z with the length of 2 or more letters. For example

HR, RJ, JS, SH, HR
HRJ, RJS, JSH, SHR
HRJS, RJSH, JSHR
HRJSH, RJSHR
HRJSHR

|[A-Z]{2,}| just returns the whole string "HRJSHR" and |[A-Z]{2}| just that ones whith a length of 2 letters. |[A-Z]{2+}| doesn't works.

Which regular expression will find all permutations of A-Z with a length of 2 ore more letters in the string?

IMHO it isn't possible with a single regex. You have to loop from 2 to the length of the string. — Toto, Feb 14 '15 at 10:40
You can check this: http://stackoverflow.com/questions/2617055/how-to-generate-all-permutations-of-a-string-in-php — Piotr Olaszewski, Feb 14 '15 at 10:56
Vote for reopen because from `ABC` OP wants to match `AB`,`BC`,`ABC` and not `AB`,`BC`,`AC`,`CB`,`CA`,`BA` as I understrand the question. — Jonny 5, Feb 14 '15 at 13:00

Jonny 5 · Accepted Answer · 2015-02-14T16:10:35.150

Could capture inside a lookahead: (?=([A-Z]{2})) would match all substrings composed of two [A-Z] such as HR,RJ,JS,SH,HR. See test at regex101.

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Combine it with a loop to get the desired result:

$str =  "HRJSHR"; $res = array();

for($i=2; preg_match_all('/(?=([A-Z]{'.$i.'}))/', $str, $out); $i++)
  $res[$i] = $out[1];

print_r($res);

See test at eval.in, outputs to:

Array
(
    [2] => Array
        (
            [0] => HR
            [1] => RJ
            [2] => JS
            [3] => SH
            [4] => HR
        )

    [3] => Array
        (
            [0] => HRJ
            [1] => RJS
            [2] => JSH
            [3] => SHR
        )

    [4] => Array
        (
            [0] => HRJS
            [1] => RJSH
            [2] => JSHR
        )

    [5] => Array
        (
            [0] => HRJSH
            [1] => RJSHR
        )

    [6] => Array
        (
            [0] => HRJSHR
        )

)

For a result without grouping by length, use:
$res = array_merge($res, $out[1]); instead of $res[$i] = $out[1];

PHP regular expression permutations

1 Answers1