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