303. Range Sum Query - Immutable

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

1. 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]).

class NumArray {
    vector<int> prefixSum;
public:
    NumArray(vector<int>& nums) {
        prefixSum.push_back(0);
        for(auto n : nums) {
            prefixSum.push_back(n + prefixSum.back());
        }
    }
    
    int sumRange(int left, int right) {
        return prefixSum[right+1] - prefixSum[left];
    }
};

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