约束和假设

• 我们正在缓存什么？
  我们正在缓存Web Query的结果
• 我们可以假设输入是有效的，还是需要对其验证？
  假设输入是有效的
• 我们可以假设它适应内存吗？
  对

编码实现

class Node(object):def __init__(self, results):self.results = resultsself.prev = Noneself.next = Noneclass LinkedList(object):del __init__(self):self.head = Noneself.tail = Nonedef move_to_front(self, node): # ...def append_to_front(self, node): # ...def remove_from_tail(self): # ...class Cache(obejct):def __init__(self, MAX_SIZE):self.MAX_SIZE = MAX_SIZEself.size = 0self.lookup = {}self.linked_list = LinkedList()def get(self, query)'''Get the stored query result from the cacheAccsssing a node updates its position to the front of the LRU list'''node = self.lookup.get(query)if node is None:return Noneself.linked_list.move_to_front(node)return node.resultsdef set(self, resuts, query):'''Set the results for the given query key in the cache.When updating an entry, updates its position to the front of the LRU listIf the entry is new and the cache is at capacity, remove the oldest entry before the new entry is added '''node = self.lookup.get(query)if node is not None:	node.results = resultsself.linked_list.move_to_front(node)else:if self.size == self.MAX_SIZEself.lookup.pop(self.linked_list.tail.query, None)self.linked_list.remove_from_tail()else:self.size += 1new_node = Node(results)self.linked_list.append_to_front(new_node)self.lookup[query] = new_node