leetcode146.py

class Node:
    def __init__(self, key=-1, val=-1, prev=None, next=None):
        self.key = key
        self.val = val
        self.prev = prev
        self.next = next

class LRUCache:

    def __init__(self, capacity: int):
        self.capacity = capacity
        self.dic = {}
        self.dummy = Node()
        self.tail = self.dummy
        
    def toTail(self, key):
        node = self.dic[key]
        if node == self.tail:
            return 
        prev = node.prev
        next = node.next
        prev.next = next
        if next:
            next.prev = prev
        node.prev = self.tail
        node.next = None
        self.tail.next = node
        self.tail = node

    def removeHead(self):
        head = self.dummy.next
        if not head:
            return 
        if head == self.tail:
            self.tail = self.dummy
        del self.dic[head.key]
        
        prev = self.dummy
        next = head.next
        prev.next = next
        if next:
            next.prev = prev
        head.next = None
        head.prev = None
            
        
    def get(self, key: int) -> int:
        if key not in self.dic:
            return -1
        self.toTail(key)
        return self.dic[key].val

    def put(self, key: int, value: int) -> None:
        if key in self.dic:
            self.dic[key].val = value
            self.toTail(key)
            return
        
        if len(self.dic) == self.capacity:
            self.removeHead()
            
        node = Node(key, value)
        self.dic[key] = node
        self.tail.next = node
        node.prev = self.tail
        self.tail = node
        

# Your LRUCache object will be instantiated and called as such:
# obj = LRUCache(capacity)
# param_1 = obj.get(key)
# obj.put(key,value)