php的一个算法问题

有这样一个数组
$arr = array(
array('a_1','a_2'),
array('b_1','b_2'),
array('c_1','c_2')
);
最后能计算成下面这个样子。
array(
'a_1,b_1,c_1',
'a_1,b_1,c_2',
'a_1,b_2,c_1',
'a_1,b_2,c_2',
'a_2,b_1,c_1',
'a_2,b_1,c_2',
'a_2,b_2,c_1',
'a_2,b_2,c_2',
);
就是让数组里的每一个元素和其他元素组合。

回复讨论(解决方案)

function foo($d) {  $r = array_pop($d);  while($d) {    $t = array();    $s = array_pop($d);    if(! is_array($s)) $s = array($s);    foreach($s as $x) {      foreach($r as $y) $t[] = array_merge(array($x), is_array($y) ? $y : array($y));    }    $r = $t;  }  return $r;}$ary = array(    'a'=>array('a_1','a_2'),    'b'=>array('b_1','b_2'),    'c'=>array('c_1','c_2'),);print_r(foo($ary));

Array(    [0] => Array        (            [0] => a_1            [1] => b_1            [2] => c_1        )    [1] => Array        (            [0] => a_1            [1] => b_1            [2] => c_2        )    [2] => Array        (            [0] => a_1            [1] => b_2            [2] => c_1        )    [3] => Array        (            [0] => a_1            [1] => b_2            [2] => c_2        )    [4] => Array        (            [0] => a_2            [1] => b_1            [2] => c_1        )    [5] => Array        (            [0] => a_2            [1] => b_1            [2] => c_2        )    [6] => Array        (            [0] => a_2            [1] => b_2            [2] => c_1        )    [7] => Array        (            [0] => a_2            [1] => b_2            [2] => c_2        ))

感谢，这个算法叫什么名来的？

叫做 笛卡尔积