lru_cache.py

__author__ = 'yangbin1729'

# 1. 基于有序字典(OrderedDict)：
from collections import OrderedDict


class LRUCache(OrderedDict):
    def __init__(self, capacity):
        super().__init__()
        self.capacity = capacity
    
    def get(self, key):
        if key not in self:
            return -1
        self.move_to_end(key)
        return self[key]
    
    def put(self, key, value):
        if key in self:
            self.move_to_end(key)
        self[key] = value
        if len(self) > self.capacity:
            self.popitem(last=False)


# 2. 基于双向链表：
class DLinkedNode():
    def __init__(self):
        self.key = 0
        self.value = 0
        self.prev = None
        self.next = None


class LinkedLRUCache():
    
    def _add_node(self, node):
        node.prev = self.head
        node.next = self.head.next
        self.head.next.prev = node
        self.head.next = node
    
    def _remove_node(self, node):
        prev = node.prev
        new = node.next
        prev.next = new
        new.prev = prev
    
    def _move_to_head(self, node):
        self._remove_node(node)
        self._add_node(node)
    
    def _pop_tail(self):
        res = self.tail.prev
        self._remove_node(res)
        return res
    
    def __init__(self, capacity):
        self.cache = {}
        self.size = 0
        self.capacity = capacity
        self.head, self.tail = DLinkedNode(), DLinkedNode()
        self.head.next = self.tail
        self.tail.prev = self.head
    
    def get(self, key):
        node = self.cache.get(key, None)
        if not node:
            return -1
        self._move_to_head(node)
        return node.value
    
    def put(self, key, value):
        node = self.cache.get(key, None)
        if not node:
            newNode = DLinkedNode()
            newNode.key = node.key
            newNode.value = node.value
            
            self.cache[key] = newNode
            self._add_node(newNode)
            
            self.size += 1
            
            if self.size > self.capacity:
                tail = self._pop_tail()
                del self.cache[tail.key]
                self.size -= 1
        else:
            node.value = value
            self._move_to_head(node)