303-easy-Range_Sum_Query_-_Immutable.js

/**
303. Range Sum Query - Immutable

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.

Example:
Given nums = [-2, 0, 3, -5, 2, -1]

sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3
Note:
You may assume that the array does not change.
There are many calls to sumRange function.
 */

/**
 * @param {number[]} nums
 */
var NumArray = function (nums) {
  var sum = 0;
  this.array = [];
  for (var i = 0; i < nums.length; i += 1) {
    sum += nums[i];
    this.array.push(sum);
  }
};

/**
 * @param {number} i
 * @param {number} j
 * @return {number}
 */
NumArray.prototype.sumRange = function (i, j) {
  if (i === 0) return this.array[j];
  return this.array[j] - this.array[i - 1];
};

/**
 * Your NumArray object will be instantiated and called as such:
 * var obj = Object.create(NumArray).createNew(nums)
 * var param_1 = obj.sumRange(i,j)
 */