php 組合算法

// 組合算法
function Combination($arr, $size = 1) {
    $len = count($arr);
    $max = pow(2,$len) - pow(2,$len-$size);
    $min = pow(2,$size)-1;

    $r_arr = array();
    for ($i=$min; $i<=$max; $i++){
        $count = 0;
        $t_arr = array();
        for ($j=0; $j<$len; $j++){
            $a = pow(2, $j);
            $t = $i&$a;
            if($t == $a){
                $t_arr[] = $arr[$j];
                $count++;
            }
        }
        if($count == $size){
            $r_arr[] = $t_arr;
        }
    }
    return $r_arr;
}
//$r = Combination(array(1,2,3,4,5,6,7),5);
//print_r($r);