LFU(最近最不常用)实现(python)

• Z时代
• 2024-01-10
• 分类：综合

from collections import defaultdict, OrderedDict
class Node:
    __slots__ = 'key', 'val', 'cnt'
    def __init__(self, key, val, cnt=0):
        self.key, self.val, self.cnt = key, val, cnt
class LFUCache:
    def __init__(self, capacity):
        self.capacity = capacity
        self.cache = {}  # type {key: node}
        self.cnt2node = defaultdict(OrderedDict)
        self.mincnt = 0
    def get(self, key, default=-1):
        if key not in self.cache:
            return default
        node = self.cache[key]
        del self.cnt2node[node.cnt][key]
        if not self.cnt2node[node.cnt]:
            del self.cnt2node[node.cnt]
        node.cnt += 1
        self.cnt2node[node.cnt][key] = node
        if not self.cnt2node[self.mincnt]:
            self.mincnt += 1
        return node.val
    def put(self, key, value):
        if key in self.cache:
            self.cache[key].val = value
            self.get(key)
            return
        if len(self.cache) >= self.capacity:
            pop_key, _pop_node = self.cnt2node[self.mincnt].popitem(last=False)
            del self.cache[pop_key]
        self.cache[key] = self.cnt2node[1][key] = Node(key, value, 1)
        self.mincnt = 1
def test():
    c = LFUCache(2)
    c.put(1, 1)
    c.put(2, 2)
    assert c.get(1) == 1
    c.put(3, 3)
    assert c.get(2) == -1
    assert c.get(3) == 3
    c.put(4, 4)
    assert c.get(1) == -1
    assert c.get(3) == 3
    assert c.get(4) == 4
if __name__ == '__main__':
    test()

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