public int CountRangeSum(int[] nums, int lower, int upper)
{
int cnt = 0;
if (nums.Length > 0)
{
MultiSet rSet = new MultiSet();
rSet.Add(0);
long sum = 0;
for (int i = 0; i < nums.Length; i++)
{
sum += (long)nums[i];
cnt += rSet.Distance(sum - (long)upper, sum - (long)lower);
rSet.Add(sum);
}
}
return(cnt);
}