Range Sum Query

class NumArray {
private:
    vector<int> sum;
    int len;
public:
    NumArray(vector<int> &nums) {
        len = nums.size();
        sum.assign(len, 0);
        for( int i = 0; i < len; i++)
            sum.push_back(move(nums[i]));

        for( int i = len-1; i >= 0; i--)
            sum[i] = sum[2*i] + sum[2*i+1];

    }

    void update(int i, int val) {
        int ind = i + len;
        int newV = val - sum[ind];
        
        // update values to the root bottom up
        while(ind > 0)
        {
            sum[ind] += newV;
            ind /= 2;
        }
    }

    int sumRange(int i, int j) {
        if(i < 0 or j >= len) return 0;
        
        // start from the leaf node and backtrack to the root getting the sum for each
        int l = i+len, r = j+len, sumR = 0;
        while(l <= r)
        {
            if(l&1) sumR += sum[l], l++;

            if(not (r&1)) sumR += sum[r], r--;

            l = l/2;
            r = r/2;
            
        }
        return sumR;
    }
};


// Your NumArray object will be instantiated and called as such:
// NumArray numArray(nums);
// numArray.sumRange(0, 1);
// numArray.update(1, 10);
// numArray.sumRange(1, 2);