Star "level" = count of stars with x' ≤ x and y' ≤ y (strictly less for equal coords? Check problem — typically includes stars with ≤ both axes, excluding itself). Sort by y ascending, process left to right.

After sorting by y, only x matters. Use Fenwick tree (BIT) over x range. For each star in order: query BIT sum up to star.x for level, then update BIT at star.x with +1.

Coordinates may be 0-based; BIT needs 1-indexed, shift x by +1. Compress x coordinates if range large (N ≤ 15000). Output array count[0..N-1] where count[l] = number of stars at level l.