374. Guess Number Higher or Lower

/** 
 * The API guess is defined in the parent class.
 * @param  num   your guess
 * @return 	     -1 if num is higher than the picked number
 *			      1 if num is lower than the picked number
 *               otherwise return 0
 * public function guess($num){}
 */

class Solution extends GuessGame {
    /**
     * @param  Integer  $n
     * @return Integer
     */
    function guessNumber($n) {
        $start = 0;
        while($start <= $n) {
            $middle = round($start + ($n - $start) / 2);
            if ($this->guess($middle) == 0) {
                return $middle;
            } elseif ($this->guess($middle) == -1) {
                 $n = --$middle;
            } else {
                $start = ++$middle;
            }
        }
    }
}