<?php
mb_internal_encoding("UTF-8");
 
function doKstring($string, $s)
{
 
    $noAnsw  = "Sorry, your string is invalid\n";
    $letters = preg_split("//u", $string, null, PREG_SPLIT_NO_EMPTY);
    foreach ($letters as $number => $letter) {
 
 
        $key = array_keys($letters, $letter);
        if (count($key) != $s) {
 
            return $noAnsw;
 
        }
    }
    sort($letters);
    $word = $letters[0];
    for ($i = 1; $i <= $s; $i++) {
 
        $key = $i * $s;
 
        $word .= $letters[$key];
    }
    $newString = $word;
    for ($i = 1; $i <= $s; $i++) {
        $new_string .= $word;
    }
 
    return $new_string . "\n";
}
print_r(doKstring(авароыафвоыф, 4));
print_r(doKstring(абвавбабв, 3));
print_r(doKstring(ахкаахкхк, 3));
print_r(doKstring(авбубббуааввууав, 4));

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