Online PHP editor | output for KlRKO

<?php function condenseDays(string $days): string { return preg_replace( '/-\K[^,]+-/', '', str_replace( ['n,t', 'e,w', 'd,t', 'u,f', 'i,s', 't,s'], ['n-t', 'e-w', 'd-t', 'u-f', 'i-s', 't-s'], $days ) ); } echo condenseDays('mon,tue,wed,thu,fri,sat') . "\n"; echo condenseDays('tue,thu,fri,sun') . "\n"; echo condenseDays('mon,tue,wed,fri,sat,sun') . "\n"; echo condenseDays('mon,thu,sun') . "\n"; echo condenseDays('tue,wed,fri,sat') . "\n"; echo condenseDays('mon,wed,fri,sun') . "\n"; echo condenseDays('mon,tue,thu,fri,sat,sun');