php数组每隔几条插入新的数据

* 这里的使用场景是从数据表里查询出来的列表，每隔一定的数量加入一条广告数据 *

<?php

// 某信息数据列表
$list = [
    ["a1" => "a1", "b1" => "b1"],
    ["a2" => "a2", "b2" => "b2"],
    ["a3" => "a3", "b3" => "b3"],
    ["a4" => "a4", "b4" => "b4"],
    ["a5" => "a5", "b5" => "b5"],
    ["a6" => "a6", "b6" => "b6"],
    ["a7" => "a7", "b7" => "b7"],
    ["a8" => "a8", "b8" => "b8"],
    ["a9" => "a9", "b9" => "b9"],
    ["a10" => "a10", "b10" => "b10"],
];

// 广告列表，尽量多查询一点出来
$listAd = [
    ["AD1" => "AD1", "AD1" => "AD1"],
    ["AD2" => "AD2", "AD2" => "AD2"],
    ["AD3" => "AD3", "AD3" => "AD3"],
    ["AD4" => "AD4", "AD4" => "AD4"],
    ["AD5" => "AD5", "AD5" => "AD5"],
    ["AD6" => "AD6", "AD6" => "AD6"],
    ["AD7" => "AD7", "AD7" => "AD7"],
    ["AD8" => "AD8", "AD8" => "AD8"],
    ["AD9" => "AD9", "AD9" => "AD9"],
];

$page = 3;
$limit = 10;
$listCount = ($page - 1) * $limit;
$insertCount = 12;

$j = floor($listCount / $insertCount);
$listNews = [];
foreach ($list as $value) {

    if ( $listCount != 0 && $listCount % $insertCount == 0 ) {

        if (isset($listAd[$j])) {
            $listNews[] = $listAd[$j];
        }
        $j++;
    }

    $listNews[] = $value;
    $listCount++;
}

echo "<pre>";
var_dump($listNews);