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Online Sandbox for SQL and PHP: Write, Run, Test, and Share SQL Queries and PHP Code
<?php
$str = "Здравствуйте!!!!! Убирррраем повторрряющиеся сииииииииииимволы. Aaaaabbbbb aaa cccccccc baac...";
echo "<pre>";
echo $str, "<br>\n";
echo preg_replace('/(.)\1+/u', '$1', $str);
echo "</pre>";