It's been a while since I used this in anger, but my recollection is that it maintains a fixed-size set of items. The same algorithm is in section 3.2 of https:

It's been a while since I used this in anger, but my recollection is that it maintains a fixed-size set of items. The same algorithm is in section 3.2 of https://erikdemaine.org/papers/NetworkStats_TR2002/paper.pdf https://erikdemaine.org/papers/NetworkStats_TR2002/paper.pdf and might be clearer there.