303. Range Sum Query Immutable - cocoder39/coco39_LC GitHub Wiki

class NumArray {
public:
    NumArray(vector<int> &nums) {
        sum.push_back(0);
        for (int i = 0; i < nums.size(); i++) {
            sum.push_back(sum[i] + nums[i]); //sum[i + 1] = sum[i] + nums[i]
        }
    }

    int sumRange(int i, int j) {
        return sum[j + 1] - sum[i];
    }
private:
    vector<int> sum;
};