function closestNumbers($arr) {
    // Write your code here
    sort($arr);
    $count_arr = count($arr);
    $temp_angka1 = [];
    $temp_angka2 = [];
    $abs =[];
    $min = 999999999;
    $hasil = [];
    
    for ($i=0; $i <= $count_arr - 2; $i++) {
        if (($arr[$i+1] - $arr[$i] < $min)) {
            $min   = $arr[$i+1] - $arr[$i];
            unset($abs);
            unset($temp_angka1);
            unset($temp_angka2);
            $abs[$i] = $min;
            $temp_angka1[$i]   = $arr[$i];
            $temp_angka2[$i+1] = $arr[$i+1];
        }
        else if ($arr[$i+1] - $arr[$i] == $min) {
            $min   = $arr[$i+1] - $arr[$i];
            $abs[$i] = $min;
            $temp_angka1[$i]   = $arr[$i];
            $temp_angka2[$i+1] = $arr[$i+1];
        }
    }
    
    $count_abs = count($abs);
    
    foreach ($abs as $key=>$val) {
        $hasil[] = $temp_angka1[$key];
        $hasil[] = $temp_angka2[$key+1];
    }
    
    return $hasil;
    
}