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<?php $string = "hello this is a string and hello but this is a string hello but this is a string and "; if (preg_match_all('~(?=(\b(\w.{9,})(?=.*?\b\2)))~u', $string, $m)) { echo array_reduce($m[1], function ($a, $b) { return strlen($a ?? '') > strlen($b ?? '') ? $a : $b; }); }
Output for 7.4.0 - 7.4.33, 8.0.1 - 8.0.30, 8.1.0 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.25, 8.4.1 - 8.4.12
hello but this is a string

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