Шамсудин Сердеров

$result = preg_split(
    '~(?<=\])|(?=\[)~',
    '[100]+[300]/[1]',
    -1,
    PREG_SPLIT_NO_EMPTY
);
// array(5) {
//   [0] => string(5) "[100]"
//   [1] => string(1) "+"
//   [2] => string(5) "[300]"
//   [3] => string(1) "/"
//   [4] => string(3) "[1]"
//}

$sum = array_sum(array_column($arr, 'price'));
foreach ($arr as &$n) {
  $n['weight'] = number_format($n['price'] / $sum * 100, 2).'%';
}