40斤西瓜3人分，求分法

<?php
$aa = range(1,40);
$bb = array();
foreach($aa as $k=>$val){
  foreach($aa as $v){
    foreach($aa as $vl){
      $sum = $val+$v+$vl;
      if($sum == 40){
        $bb[$k][0] = $val;
        $bb[$k][1] = $v;
        $bb[$k][2] = $vl;
      }
    }
  }
}
echo ‘<pre>‘;
print_r($bb);
exit;
?>

Array
(
  [0] => Array
    (
      [0] => 1
      [1] => 38
      [2] => 1
    )
  [1] => Array
    (
      [0] => 2
      [1] => 37
      [2] => 1
    )
  [2] => Array
    (
      [0] => 3
      [1] => 36
      [2] => 1
    )
  [3] => Array
    (
      [0] => 4
      [1] => 35
      [2] => 1
    )
  [4] => Array
    (
      [0] => 5
      [1] => 34
      [2] => 1
    ) 
   ...
   ...
   ...