67 lines
1.9 KiB
Python
67 lines
1.9 KiB
Python
class Node(object):
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def __init__(self, results):
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self.results = results
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self.next = next
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class LinkedList(object):
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def __init__(self):
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self.head = None
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self.tail = None
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def move_to_front(self, node):
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pass
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def append_to_front(self, node):
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pass
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def remove_from_tail(self):
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pass
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class Cache(object):
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def __init__(self, MAX_SIZE):
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self.MAX_SIZE = MAX_SIZE
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self.size = 0
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self.lookup = {} # key: query, value: node
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self.linked_list = LinkedList()
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def get(self, query):
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"""Get the stored query result from the cache.
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Accessing a node updates its position to the front of the LRU list.
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"""
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node = self.lookup.get(query)
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if node is None:
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return None
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self.linked_list.move_to_front(node)
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return node.results
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def set(self, results, query):
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"""Set the result for the given query key in the cache.
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When updating an entry, updates its position to the front of the LRU list.
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If the entry is new and the cache is at capacity, removes the oldest entry
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before the new entry is added.
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"""
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node = self.lookup.get(query)
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if node is not None:
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# Key exists in cache, update the value
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node.results = results
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self.linked_list.move_to_front(node)
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else:
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# Key does not exist in cache
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if self.size == self.MAX_SIZE:
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# Remove the oldest entry from the linked list and lookup
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self.lookup.pop(self.linked_list.tail.query, None)
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self.linked_list.remove_from_tail()
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else:
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self.size += 1
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# Add the new key and value
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new_node = Node(results)
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self.linked_list.append_to_front(new_node)
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self.lookup[query] = new_node
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