0303-range-sum-query-immutable.cpp

/*
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]).

*/


class NumArray {
public:
    vector<int> prefixSum;
    NumArray(vector<int>& nums) {
        int count=0;
        for(int i=0;i<nums.size();i++){
            count+=nums[i];
            prefixSum.push_back(count);
        }
    }
    
    int sumRange(int left, int right) {
        int answer=prefixSum[right];

        if(left-1>=0){
            answer-=prefixSum[left-1];
        }
        return answer;
    }
};

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