求高效率算法找

$a = array(
    'A' => array(1,2,3,4,5,6),
    'B' => array(1,7,8,9),
    'C' => array(1,6,7,8,9),
)
    
    
$b = array(
    '2','4'
)
    求高效算法找出 $b数组  属于数组 $a  A、B、C的那一项的子集，注 $a,$b 数量不确定  

$a = array(
    'A' => array(1,2,3,4,5,6),
    'B' => array(1,7,8,9),
    'C' => array(1,6,7,8,9),
);
     
$b = array(
    '2','4'
);

$r = array_filter($a, function($t) use ($b) {
  return array_intersect($b, $t) == $b;
});

print_r($r);

Array
(
    [A] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
            [3] => 4
            [4] => 5
            [5] => 6
        )

)