643. maximum average subarray i

class  {
    public double findMaxAverage(int[] nums, int k) {
        int max = 0;
      for (int i = 0; i < k; i++) {
       max += nums[i];
      }
      int sum = max;
        for (int l  = 0, r = k; r < nums.length; l++, r++) {
            sum += nums[r] - nums[l];//每前进增加一个，去掉头部一个，得出一个新的和
           max = Math.max(max, sum);//比较最大值和新的值哪个大
     }
        return (double)max / k;
    }
}