Online PHP editor | refs for ANC7P

<?php $trim = function($str) { return preg_replace('~$+(\(((?:[^()]*|(?1))*)$)\)+|($(?:[^()]*|\g{-1})*$)~', '$2$3', $str); }; echo $trim('((((A))))'), "\n"; echo $trim('(((((B+C)*A)*(F))))'), "\n"; echo $trim('(A+B)(B+C)'), "\n"; echo $trim('(((((B+C)*A))))'), "\n"; echo str_repeat('-',15), PHP_EOL; echo $trim('((A+B)+C)'), "\n"; echo $trim('(((A+B))+C)'), "\n"; echo $trim('((((A+B)+C))'), "\n"; echo $trim('(A+(B+C))'), "\n"; echo $trim('(A+((B+C)))'), "\n";