public int CountRangeSumSegTree(int[] nums, int lower, int upper)
{
// prefix sum; use long to avoid overflow
var sums = new long[nums.Length + 1];
for (int i = 0; i < nums.Length; i++)
{
sums[i + 1] = sums[i] + nums[i];
}
// intially the Count of all prefix sum is 0; use set to remove duplicates
var tree = new SegmentCountTree(new SortedSet <long>(sums).ToArray());
int ret = 0;
for (int i = 0; i < nums.Length; i++)
{
// set the Count of previous prefix sum
tree.Update(sums[i]);
// query the count of j, where lower <= sum[i] - sum[j] <= upper, that is sum[i] - upper <= sum[j] <= sum[i] - lower
ret += tree.Query(sums[i + 1] - upper, sums[i + 1] - lower);
}
return(ret);
}
public IList <int> CountSmallerSegtree(int[] nums)
{
var tree = new SegmentCountTree(new SortedSet <int>(nums).ToArray());
var ret = new int[nums.Length];
for (int i = nums.Length - 1; i >= 0; i--)
{
ret[i] = tree.Query(nums[i]);
tree.Update(nums[i]);
}
return(ret);
}
