Lottery Algorithm

<?php

class Lottery
{
    private $start;
    private $end;
    public $tempBalls = [];

    public function __construct($start = 1, $end = 49)
    {
        $this->start = $start;
        $this->end = $end;
    }

    public function balls($num = 5)
    {
        $balls = range($this->start, $this->end);
        $results = [];

        do {
            $results[] = $this->randBall($balls);
        } while (count($results) < $num);

        $result = implode(', ', $results);
        $this->tempBalls = [];

        return $result;
    }

    private function randBall($range)
    {
        $ball = $range[mt_rand(0, count($range) - 1)];

        if (!in_array($ball, $this->tempBalls)) {
            $this->tempBalls[] = $ball;
        } else {
            return $this->randBall($range);
        }

        return $ball;
    }
}