brackets.php

<?php
$s = "((a+b*d)*(x/2))*(1+(y+(x-2)/10))";
$b = [];
$j = 0;
$stack = [];

for ($i = 0; $i < strlen($s); $i++)
{	
	if ($s[$i] == '(')
	{		
		$b[++$j] = '';
	}
	elseif ($s[$i] == ')')
	{		
		$stack[] = ($b[$j--] .= ')');	
	}
	for ($k = 1; $k <= $j; $k++)
	{
		$b[$k] .= $s[$i];
	}
}
echo $s.PHP_EOL;
print_r($stack);
echo PHP_EOL;
?>