如何使用正则表达式在php中找到完全相同的序列？

$string = "This is a test test string. It contains duplicate duplicate words.";
$pattern = "/\b(\w+)\b/";

preg_match_all($pattern, $string, $matches);

$matchedSequences = array();
foreach ($matches[0] as $match) {
    if (isset($matchedSequences[$match])) {
        $matchedSequences[$match]++;
    } else {
        $matchedSequences[$match] = 1;
    }
}

foreach ($matchedSequences as $sequence => $count) {
    if ($count > 1) {
        echo "Found duplicate sequence: " . $sequence . " (Count: " . $count . ")" . PHP_EOL;
    }
}

Found duplicate sequence: test (Count: 2)
Found duplicate sequence: duplicate (Count: 2)