$arr = array(4,7,0,2,4,5,6,9,1,2,3,4);
$counter = 1;
for($i = 0; $i < count($arr) - 1; $i ++) {
   if ($arr[$i + 1] == $arr[$i] + 1) {
      $counter ++;
      if ($counter == 3) {
         echo "<pre>找到连续值的数字：\n[".($i - 1)."]=>{$arr[$i - 1]}\n[".$i."]=>{$arr[$i]}\n[".($i + 1)."]=>{$arr[$i + 1]}\n</pre>";
      }
   }
   else $counter = 1;
}