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
python
class Node(object):
def __init__(self, results):
self.results = results
self.prev = None
self.next = None
class LinkedList(object):
del __init__(self):
self.head = None
self.tail = None
def 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_SIZE
self.size = 0
self.lookup = {}
self.linked_list = LinkedList()
def get(self, query)
'''
Get the stored query result from the cache
Accsssing a node updates its position to the front of the LRU list
'''
node = self.lookup.get(query)
if node is None:
return None
self.linked_list.move_to_front(node)
return node.results
def 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 list
If 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 = results
self.linked_list.move_to_front(node)
else:
if self.size == self.MAX_SIZE
self.lookup.pop(self.linked_list.tail.query, None)
self.linked_list.remove_from_tail()
else:
self.size += 1
new_node = Node(results)
self.linked_list.append_to_front(new_node)
self.lookup[query] = new_node