diff --git a/other/least_recently_used.py b/other/least_recently_used.py new file mode 100644 index 000000000..2932e9c18 --- /dev/null +++ b/other/least_recently_used.py @@ -0,0 +1,62 @@ +from abc import abstractmethod +import sys +from collections import deque + +class LRUCache: + """ Page Replacement Algorithm, Least Recently Used (LRU) Caching.""" + + dq_store = object() # Cache store of keys + key_reference_map = object() # References of the keys in cache + _MAX_CAPACITY: int = 10 # Maximum capacity of cache + + @abstractmethod + def __init__(self, n: int): + """ Creates an empty store and map for the keys. + The LRUCache is set the size n. + """ + self.dq_store = deque() + self.key_reference_map = set() + if not n: + LRUCache._MAX_CAPACITY = sys.maxsize + elif n < 0: + raise ValueError('n should be an integer greater than 0.') + else: + LRUCache._MAX_CAPACITY = n + + def refer(self, x): + """ + Looks for a page in the cache store and adds reference to the set. + Remove the least recently used key if the store is full. + Update store to reflect recent access. + """ + if x not in self.key_reference_map: + if len(self.dq_store) == LRUCache._MAX_CAPACITY: + last_element = self.dq_store.pop() + self.key_reference_map.remove(last_element) + else: + index_remove = 0 + for idx, key in enumerate(self.dq_store): + if key == x: + index_remove = idx + break + self.dq_store.remove(index_remove) + + self.dq_store.appendleft(x) + self.key_reference_map.add(x) + + def display(self): + """ + Prints all the elements in the store. + """ + for k in self.dq_store: + print(k) + +if __name__ == "__main__": + lru_cache = LRUCache(4) + lru_cache.refer(1) + lru_cache.refer(2) + lru_cache.refer(3) + lru_cache.refer(1) + lru_cache.refer(4) + lru_cache.refer(5) + lru_cache.display()