php-combination

一个数组元素的多重组合,基本的原理是：
假设是元素A B C,这三个元素的组合可以分别对应如下：

A	B	C
0	0	1
0	1	0
1	0	0
0	1	1
...

从这里看出，二进制数从1到7就是ABC的全部组合情况，那就是说组合的总个数应该是2^n，只要求出2^n的值，
那相应的每种组合情况就可以用二进制来还原， 这里用php实现了基本的代码：
function test($price,$words)
{
$num = count($words);
$total = pow(2, $num);
$result = array();
for ($i = 1; $i < $total; $i++)
{
$res = 1;
for ($j = 0; $j < $num; $j++)
{
if (pow(2, $j) & $i) $res=$res*$words[$j];
}
$result[] = floor(($res*$price*100))/100;
}
return $result;
}
?>
结果如下： Array ( [0] => 1209.74 [1] => 1222.08 [2] => 1197.64 [3] => 1197.39 [4] => 1173.45 [5] => 1185.42 [6] => 1161.71 [7] => 1185.05 [8] => 1161.35 [9] => 1173.2 [10] => 1149.74 [11] => 1149.5 [12] => 1126.51 [13] => 1138 [14] => 1115.24 [15] => 1172.71 [16] => 1149.25 [17] => 1160.98 [18] => 1137.76 [19] => 1137.52 [20] => 1114.77 [21] => 1126.15 [22] => 1103.63 [23] => 1125.8 [24] => 1103.28 [25] => 1114.54 [26] => 1092.25 [27] => 1092.02 [28] => 1070.18 [29] => 1081.1 [30] => 1059.48 )