146. LRU缓存机制

傷城~ 2022-05-13 18:40 215阅读 0赞

运用你所掌握的数据结构，设计和实现一个 LRU (最近最少使用) 缓存机制。它应该支持以下操作： 获取数据 get 和 写入数据 put 。

获取数据 get(key) - 如果密钥 (key) 存在于缓存中，则获取密钥的值（总是正数），否则返回 -1。  
写入数据 put(key, value) - 如果密钥不存在，则写入其数据值。当缓存容量达到上限时，它应该在写入新数据之前删除最近最少使用的数据值，从而为新的数据值留出空间。

进阶:

你是否可以在 O(1) 时间复杂度内完成这两种操作？

LRUCache cache = new LRUCache( 2 /* 缓存容量 */ );
    
    cache.put(1, 1);
    cache.put(2, 2);
    cache.get(1);       // 返回  1
    cache.put(3, 3);    // 该操作会使得密钥 2 作废
    cache.get(2);       // 返回 -1 (未找到)
    cache.put(4, 4);    // 该操作会使得密钥 1 作废
    cache.get(1);       // 返回 -1 (未找到)
    cache.get(3);       // 返回  3
    cache.get(4);       // 返回  4

### python ###

class LRUCache(object):
        def __init__(self, capacity):
            self.capacity = capacity
            self._cache = []   
            self._cache_look_up = { }
    
        def get(self, key):
            if key in self._cache_look_up:
                self._cache.remove(key)
                self._cache.append(key)
                return self._cache_look_up[key]
            else:
                return -1 
            
        def put(self, key, value):
            if key in self._cache_look_up:
                self._cache_look_up[key] = value
                self._cache.remove(key)
                self._cache.append(key)
                return 
            else:
                
                if len(self._cache) == self.capacity:
                    del_key = self._cache[0]
                    self._cache = self._cache[1:]
                    del self._cache_look_up[del_key]
                    
                self._cache.append(key)
                self._cache_look_up[key] = value

### python O(1) ###

class LinkNode(object):
    
        def __init__(self, key, val, prev_node=None, next_node=None):
            self.key = key
            self.val = val
            self.prev = prev_node
            self.next = next_node
    
    
    class DoubleLinkList(object):
    
        def __init__(self, capacity):
            self.capacity = capacity
            self.size = 0
    
            self.head = None
            self.tail = None
    
        def append(self, node):
            """ :param node: :return: append a node to the double link list last """
            if self.size == self.capacity:
                raise ValueError("The double link list has been full.")
    
            self.size += 1
    
            if self.head is None:
                self.head = self.tail = node
                return
    
            self.tail.next = node
            node.prev = self.tail
            self.tail = node
    
        def delete(self, node):
            """ :param node: :return node: delete a node in double link list. switch(node): 1.node == self.head 2.node == self.tail 3.node in the double link list middle """
            if self.size == 0:
                raise ValueError("can not delete empty double link list")
    
            self.size -= 1
    
            if node == self.head:
                if node.next:
                    node.next.prev = None
    
                self.head = node.next
            elif node == self.tail:
                if node.prev:
                    node.prev.next = None
    
                self.tail = node.prev
            else:
                node.prev.next = node.next
                node.next.prev = node.prev
    
            return node
    
    
    class LRUCache(object):
    
        def __init__(self, capacity):
            self.capacity = capacity
            self.cache_look_up = { }
            self.cache_list = DoubleLinkList(capacity)
    
        def get(self, key):
            if key not in self.cache_look_up:
                return -1
    
            node = self.cache_look_up[key]
            self.cache_list.delete(node)
            self.cache_list.append(node)
    
            return node.val
    
        def put(self, key, value):
            if key in self.cache_look_up:
                node = self.cache_look_up[key]
                node.val = value
                self.cache_list.delete(node)
                self.cache_list.append(node)
            else:
                if self.capacity == self.cache_list.size:
                    head_node = self.cache_list.delete(self.cache_list.head)
                    del self.cache_look_up[head_node.key]
    
                new_node = LinkNode(key, value)
                self.cache_look_up[key] = new_node
                self.cache_list.append(new_node)

参考：[https://blog.csdn.net/laughing2333/article/details/70231547][https_blog.csdn.net_laughing2333_article_details_70231547]

[https_blog.csdn.net_laughing2333_article_details_70231547]: https://blog.csdn.net/laughing2333/article/details/70231547