Leetcode 303 - Range sum query - Immutable

Note:

  • Lots of calls will be made, it’s not clever to calculate each call.
  • Make an array for sum[0, i]
  • Do deduction betwen arr[right] - arr[left - 1].
  • Make arr[left - 1] === 0 when left - 1 < 0.

Question:

Given an integer array nums, handle multiple queries of the following type:

  • Calculate the sum of the elements of nums between indices left and right inclusive where left <= right.

Implement the NumArray class:

  • NumArray(int[] nums) Initializes the object with the integer array nums.
  • int sumRange(int left, int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + … + nums[right]).

Example:

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Input
["NumArray", "sumRange", "sumRange", "sumRange"]
[[[-2, 0, 3, -5, 2, -1]], [0, 2], [2, 5], [0, 5]]
Output
[null, 1, -1, -3]

Explanation
NumArray numArray = new NumArray([-2, 0, 3, -5, 2, -1]);
numArray.sumRange(0, 2); // return (-2) + 0 + 3 = 1
numArray.sumRange(2, 5); // return 3 + (-5) + 2 + (-1) = -1
numArray.sumRange(0, 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3

Code:

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/**
* @param {number[]} nums
*/
var NumArray = function(nums) {
const array = [...Array(nums.length).fill(0)];
for (let i = 0; i < array.length; i++) {
if (i === 0) {
array[i] = nums[i];
} else {
array[i] = array[i - 1] + nums[i];
}
}
this.array = array;
};

/**
* @param {number} left
* @param {number} right
* @return {number}
*/
NumArray.prototype.sumRange = function(left, right) {
const array = this.array;
return array[right] - (left - 1 < 0 ? 0 : array[left - 1]);
};

/**
* Your NumArray object will be instantiated and called as such:
* var obj = new NumArray(nums)
* var param_1 = obj.sumRange(left,right)
*/