def __init__(self, maxlen, **kwargs):
# ARC has two caches: a recency cache and a frequency cache
self._recency_cache_top = LinkedSet() # paper: T_1
self._recency_cache_bottom = LinkedSet() # paper: B_1
self._frequency_cache_top = LinkedSet() # paper: T_2
self._frequency_cache_bottom = LinkedSet() # paper: B_2
self._maxlen = int(maxlen) # paper: c
if self._maxlen <= 0:
raise ValueError('maxlen must be positive')
# _p is the target number of elements for the recency cache top
# which means that _maxlen - _p is the target number of elements for the frequency cache top
# It is the target number since it will be a real number at some point and not a natural number.
self._p = 0
