public:

int countRangeSum(vector<int>& nums, int lower, int upper) {

vector<long> sums(nums.size()+1, 0);

for (int i = 0; i != nums.size(); i++)

sums[i+1] = sums[i] + nums[i];

return countRange(sums, 0, nums.size()+1, lower, upper);

}

private:

int countRange(vector<long>& sums, int start, int end, int lower, int upper) {

if (end - start <= 1)

return 0;

int mid = start + (end - start) / 2;

long count = countRange(sums, start, mid, lower, upper) + countRange(sums, mid, end, lower, upper);

int r = mid, l = mid;

for (int i = start; i != mid; i++) {

while (l < end && sums[l] - sums[i] < lower)

l++;

while (r < end && sums[r] - sums[i] <= upper)

r++;

count += r - l;

}

inplace_merge(sums.begin()+start, sums.begin()+mid, sums.begin()+end);

return count;

}