排列组合算法

<code>$arr = [
    'a'=>[0,1,2,3],
    'b'=>[0,1,2,3,6,7],
    'c'=>[1,2,3,4,7,8,9],
    'd'=>[6,8,1,3,5]
];
//上面组成的新数组:
$new = [
    count($arr[a]) * count($arr[b]),
    count($arr[a]) * count($arr[c]),
    count($arr[a]) * count($arr[d]),
    count($arr[b) * count($arr[c]),
    count($arr[b) * count($arr[d]),
    count($arr[c) * count($arr[d])
];
//最后把new数组里面的值全部相加</code>

<code>$arr = [
    'a'=>[0,1,2,3],
    'b'=>[0,1,2,3,6,7],
    'c'=>[1,2,3,4,7,8,9],
    'd'=>[6,8,1,3,5]
];
//上面组成的新数组:
$new = [
    count($arr[a]) * count($arr[b]),
    count($arr[a]) * count($arr[c]),
    count($arr[a]) * count($arr[d]),
    count($arr[b) * count($arr[c]),
    count($arr[b) * count($arr[d]),
    count($arr[c) * count($arr[d])
];
//最后把new数组里面的值全部相加</code>

<code><?php
$arr = [
    'a'=>[0,1,2,3],
    'b'=>[0,1,2,3,6,7],
    'c'=>[1,2,3,4,7,8,9],
    'd'=>[6,8,1,3,5]
];

$arr_len = array();
foreach($arr as $item) {
    $arr_len[] = count($item);
}
// 以上循环可以统计字数组的长度

$res = 0; // 要输出的结果
$c_arr_len = $arr_len;
foreach($arr_len as $k1=>$v1) {
    unset($c_arr_len[$k1]); // 处理了一个数之后删除
    if(count($c_arr_len)>0) {
        foreach($c_arr_len as $k2=>$v2) {
            $res += ($v1*$v2);
        }
    }
}
var_dump($res);//得到结果，其实不需要产生你那个$new数组</code>