303. Range Sum Query - Immutable

class NumArray {
    private:
    vector<int> accuSum;
public:
    NumArray(vector<int> nums) {
        int accuSumVal=0;
        accuSum.push_back(accuSumVal);
        for(int i = 0;i<nums.size();++i){
            accuSumVal+=nums[i];
            accuSum.push_back(accuSumVal);
        }

    }

    int sumRange(int i, int j) {
       int ret = accuSum[j+1]-accuSum[i];
        return ret;
    }
};

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray obj = new NumArray(nums);
 * int param_1 = obj.sumRange(i,j);
 */