Fork Copy <?php function kill($array) { $length = count($array); $output = []; for ($i = 0; $i < $length; $i+=2) { $output[] = $array[$i]; echo $array[$i] . ', '; usleep(100 * 1000); if ($i + 1 < $length) { echo "[{$array[$i + 1]}], "; } usleep(100 * 1000); } echo PHP_EOL; return $output; } $input = range(1, 100); $output = kill($input); while (count($output) > 1) { $newInput = array_reverse($output); if ($newInput[0] == end($input)) { $input = array_merge([$newInput[0]], array_reverse(array_slice($newInput, 1))); } else { $input = $output; echo $newInput[0] . ' -> '; } $output = kill($input); } echo end($output);