php - Check if in a set of numbers, a number n is equal to sum of its subset -


i have array : 

$permissionvals = array (1,2,4,8,16,32);

and variable 

$effectivepermission = 13;

i need check whether variable equal sum of subset of given array of numbers in optimized way.

subset sum doesn't seems work me here.

assuming $permissionvals contains powers of 2, can use bit comparison:

$permissionvals = array(1,2,4,8,16,32); $target = 13; $res = array();  foreach ($permissionvals $val) {     if ($target & $val) $res[] = $val; }  if (array_sum($res) == $target)     print_r($res); else      echo 'the message want';

a variant stop foreach loop when sum reached. (useful if $permissionvals big):

$sum = 0; $message = 'the message want';  foreach ($permissionvals $val) {     if ($target & $val) {         $res[] = $val;         $sum += $val;     }     if ($sum == $target) {     $message = '';     print_r($res);     break;     } }  echo $message;

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