$length = $_GET['length'];
$proto = $_GET['proto'];
$dead = $_GET['dead'];

$dict = file("wordlist/" . $length . "_letters.txt", FILE_IGNORE_NEW_LINES);

$exp = '/^' . str_replace('*', '\w{1}', $proto) . '$/u';
$words = array_filter($dict, function ($v) use ($exp, $dead) {
    $dw = true;
    foreach (array_diff(preg_split('//u', $dead), ['']) as $d) {
        if (preg_match('/' . $d . '/u', $v)) {
            $dw = false;
            break;
        };
    }
    return (preg_match($exp, $v) && $dw);
});

$letters = [];
foreach ($words as $v) {
    $imp = implode('|', preg_split('//u', str_replace('*', '', $proto)));
    foreach (array_diff(preg_split('//u', preg_replace('/(' . $imp . ')/u', '', $v)), ['']) as $w) {
        $letters[] = $w;
    }
}

$percentageLetters = [];
$count = count($words);
foreach (array_unique($letters) as $v) {
    $c = 0;
    foreach ($words as $w) {
        if (preg_match('/' . $v . '/u', $w)) $c++;
    }
    $percentageLetters[] = ['letter' => $v, 'percent' => round(($c / $count * 100), 1) . '%'];
}
uasort($percentageLetters, function ($a, $b) {
    return ((float)$a['percent'] > (float)$b['percent']) ? -1 : 1;
});

/* массив букв со 100% вероятностью */
$arrPercent100 = array_values(array_filter($percentageLetters, function($data) {
    return ((float)$data['percent'] == 100);
}));
/* буква с самым большим процентом */
$mostLetter = (!count($arrPercent100)) ? array_shift($percentageLetters) : [];

$ret = ['words' => $words, 'letters' => array_values($percentageLetters)];
print_r($ret);