class NumArray {

    private $nums;
    private $sum_arr;

    /**
     * @param Integer[] $nums
     */
    function __construct($nums) {
        $this->nums = $nums;
        $sum = 0;
        $sum_arr =  [];
        for ($s=0;$s<count($this->nums);$s++){
            $sum += ($this->nums)[$s];
            $sum_arr[$s] = $sum;
            $this->sum_arr = $sum_arr;
        }
    }

    function sumRange($i, $j) {
        $sum_arr = $this->sum_arr;
        if ($i==0) return $sum_arr[$j];
        return $sum_arr[$j] - $sum_arr[$i-1];
//        return array_sum(array_slice($this->nums,$i,($j-$i)+1));
    }
}