求高效率算法找

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

$a = array(<br />    'A' => array(1,2,3,4,5,6),<br />    'B' => array(1,7,8,9),<br />    'C' => array(1,6,7,8,9),<br />);<br />     <br />$b = array(<br />    '2','4'<br />);<br /><br />$r = array_filter($a, function($t) use ($b) {<br />  return array_intersect($b, $t) == $b;<br />});<br /><br />print_r($r);

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