3v4l.org

run code in 200+ PHP versions simultaneously
<?php $s = "01001010101101111011101001010100010101101010101010101101101010010110110110"; $n = 10; for($a=$b=$c=0;(($d=@substr_count($s,1,$a,$n))>$c&&(($b=$a)&&($c=$d)))||$a<strlen($s);$a++);echo $b;
based on dQ7Qi
Output for 5.1.0 - 7.4.0
10
Output for 4.3.0 - 5.0.5
0