146. LRU Cache [Medium] 链表LRU

class Node(object):
    def __init__(self, key, val):
        self.key = key
        self.val = val
        self.prev = None
        self.next = None
        
class LRUCache(object):

    def __init__(self, capacity):
        """
        :type capacity: int
        """
        self.head = Node(None, None)
        self.tail = Node(None, None)
        self.size = 0
        self.capacity = capacity
        self.head.next = self.tail 
        self.tail.prev = self.head
        self.position = {}
        self.record = {}

    def updateOrder(self, node):
        node.prev.next = node.next
        node.next.prev = node.prev
        node.prev = self.tail.prev
        self.tail.prev.next = node
        node.next = self.tail
        self.tail.prev = node
        return node
        
        
    def get(self, key):
        """
        :type key: int
        :rtype: int
        """
        if key in self.record:
            self.position[key] = self.updateOrder(self.position[key])
            return self.record[key]
        else:
            return -1
        

    def put(self, key, value):
        """
        :type key: int
        :type value: int
        :rtype: None
        """
        if key in self.record:
            self.record[key] = value
            node = self.position[key]
            node = self.updateOrder(node)
            node.val = value
        else:
            if self.size == self.capacity:
                self.size -= 1
                del self.position[self.head.next.key]
                del self.record[self.head.next.key]
                self.head.next = self.head.next.next
                self.head.next.prev = self.head
            self.size += 1
            node = Node(key, value)
            self.tail.prev.next = node
            node.prev = self.tail.prev
            node.next = self.tail
            self.tail.prev = node
            self.record[key] = value
            self.position[key] = node