LRU cache design

Question

Least Recently Used (LRU) Cache is to discard the least recently used items first How do you design and implement such a cache class? The design requirements are as follows:

Answer 1

Working of LRU Cache

Discards the least recently used items first. This algorithm requires keeping track of what was used when which is expensive if one wants to make sure the algorithm always discards the least recently used item. General implementations of this technique require keeping "age bits" for cache-lines and track the "Least Recently Used" cache-line based on age-bits. In such an implementation, every time a cache-line is used, the age of all other cache-lines changes.

The access sequence for the below example is A B C D E C D B.

class Node: def init(self, k, v): self.key = k self.value = v self.next = None self.prev = None class LRU_cache: def init(self, capacity): self.capacity = capacity self.dic = dict() self.head = Node(0, 0) self.tail = Node(0, 0) self.head.next = self.tail self.tail.prev = self.head def _add(self, node): p = self.tail.prev p.next = node self.tail.prev = node node.next = self.tail node.prev = p def _remove(self, node): p = node.prev n = node.next p.next = n n.prev = p def get(self, key): if key in self.dic: n = self.dic[key] self._remove(n) self._add(n) return n.value return -1 def set(self, key, value): n = Node(key, value) self._add(n) self.dic[key] = n if len(self.dic) > self.capacity: n = self.head.next self._remove(n) del self.dic[n.key] cache = LRU_cache(3) cache.set('a', 'apple') cache.set('b', 'ball') cache.set('c', 'cat') cache.set('d', 'dog') print(cache.get('a')) print(cache.get('c'))