/**

* @filename NumArray.js

* @author 56

* @description https://leetcode-cn.com/problems/range-sum-query-immutable/

*/

/**

* @param {number[]} nums

*/

var NumArray = function (nums) {

this.nums = nums

const sums = [0]

this.sums = sums

for (let i = 1, len = nums.length + 1; i < len; i++) {

sums[i] = sums[i - 1] + nums[i - 1]

}

}

/**

* 1. 看了题解. 用前缀和来优化

* @param {number} i

* @param {number} j

* @return {number}

*/

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

return this.sums[j + 1] - this.sums[i]

// const nums = this.nums

// if (!Array.isArray(nums)) return 0

// const len = this.nums.length

// if (len === 0 || i > len) return 0

// let sum = 0

// for (let k = i; k <= j && k < len; k++) sum += nums[k]

// return sum

}

/**

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

* var obj = new NumArray(nums)

* var param_1 = obj.sumRange(i,j)

*/

console.info(new NumArray([1, 2, 3, 4]).sumRange(1, 2))