/**

 * @constructor

 * @param {number[]} nums

 */

var NumArray = function(nums) {

    this.nums = nums;

    this.cache = [];

    var acc = 0;

    for (var i = 0; i < nums.length; i++) {

        acc += nums[i];

        this.cache.push(acc);

    }

};

/**

 * @param {number} i

 * @param {number} j

 * @return {number}

 */

NumArray.prototype.sumRange = function(i, j) {

    if (this.cache.length === 0) return 0;

    return this.cache[j] - this.cache[i] + this.nums[i];

};

/**

 * Your NumArray object will be instantiated and called as such:

 * var numArray = new NumArray(nums);

 * numArray.sumRange(0, 1);

 * numArray.sumRange(0, 2);

 */