試著把Model和View分離之後，原先解決掉重覆生成的效能就被吃掉的第二版。

gistfile1.txt

<?php
// 100 以內加減法正整數答案
// 美觀度就別管了XD
header('Content-Type: text/html; charset=utf-8');
ini_set('memory_limit', '1024M');
ini_set('display_errors', 1);
ini_set('xdebug.max_nesting_level', 0);
set_time_limit(0);
error_reporting(E_ALL);
define("DEBUG", true);
$answers = "";
$count = 1;
$howmany = 100;

$time_start = microtime(true);
?>
<style>
    div {
        font-family: Segoe UI Light
    }
    .n {
        font-size: 25px
    }
    .s{
        font-size: 70px
    }
</style><div class='n'>
<?php
function generate(){
    global $howmany;
    global $count;

    $answer = [];

    // 不要這樣做，這樣會沒辦法直接意識howmany有沒有底線的差異
    //$howmany_ = $howmany + 1;


    // 用迴圈會比用遞迴少上一些記憶體
    while($count <= $howmany){

        $operate = rand(0, 1); // 先決定OP，這樣可以控制第二個數字的範圍

        $number_one = rand(40, 80);
        if($operate == 1){
            $rand_two = $number_one - 5;
            $number_diff = rand(20, $rand_two); // rand(20, 35) ~ rand(20, 75)  <<== Answer desu
            $number_two = $number_one - $number_diff;
            $answer[] = ['operation' => '-', 'number' => [$number_one,$number_two,$number_diff]];
        }else{
            $number_ans = rand($number_one, 99);
            $number_two = $number_ans - $number_one;
            $answer[] = ['operation' => '-', 'number' => [$number_one,$number_two,$number_ans]];
        }

        $count++;
    }
    return $answer;
}

$answer = generate();

foreach($answer as $ln => $line){
?>
  <?=$ln?>. &nbsp;&nbsp;&nbsp;<?=$line['number'][0].' '.$line['operation'].' '.$line['number'][1]?> = <br/>
<?php
}

// 一堆BR的原因是因為湊一整頁，把答案印在新的紙上（100題剛好）
?>
<!-- 這邊說不定用CSS解決會比較好? -->

<br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br />
</div>

<div class='s'>Answers</div>
<div class='n'>
<?php
foreach($answer as $ln => $line){
?>
  <?=$ln.'. &nbsp;&nbsp;&nbsp;'. $line['number'][0].' '.$line['operation'].' '.$line['number'][1].' = '.$line['number'][2]?><br/>
<?php
}
?>
</div>
<?php
if( DEBUG ){
    echo "<br />";
    $time_end = microtime(true);
    $time = $time_end - $time_start;
    echo $time;
}

我還在試著讀懂L47想做什麼