Was going to mention Fenwick Tree here as well, but since you've already did, I'll just add that this is IMO a great introduction to Fenwick Trees: https://www.

Was going to mention Fenwick Tree here as well, but since you've already did, I'll just add that this is IMO a great introduction to Fenwick Trees: https://www.youtube.com/watch?v=kPaJfAUwViY https://www.youtube.com/watch?v=kPaJfAUwViY