146. LRU Cache

class LRUCache:
    def __init__(self, capacity: int):
        self.capacity = capacity
        self.cache = {}

    def get(self, key: int) -> int:
        if key in self.cache:
            self.cache[key] = self.cache.pop(key)
            return self.cache[key]
        return -1
        
    def put(self, key: int, value: int) -> None:
        if key in self.cache:
            del self.cache[key]
        if len(self.cache) == self.capacity:
            self.cache.pop(next(iter(self.cache)))
        self.cache[key] = value

class Node:
    def __init__(self, key: int = None, value: int = None):
        self.key = key
        self.value = value
        self.prev = None
        self.next = None

class DLL:
    def __init__(self):
        self.head = Node()
        self.tail = Node()
        self.head.next = self.tail
        self.tail.prev = self.head

    def insert(self, node: Node) -> None:
        pre, nxt = self.head, self.head.next
        node.prev = pre
        node.next = nxt
        pre.next = node
        nxt.prev = node
    
    def remove(self, node: Node) -> int:
        pre, nxt = node.prev, node.next
        pre.next = nxt
        nxt.prev = pre
        return node.key

    def last(self) -> Node:
        return self.tail.prev
    
class LRUCache:
    def __init__(self, capacity: int):
        self.capacity = capacity
        self.cache = {}
        self.list = DLL()

    def get(self, key: int) -> int:
        if key in self.cache:
            node = self.cache[key]
            self.list.remove(node)
            self.list.insert(node)
            return node.value
        return -1

    def put(self, key: int, value: int) -> None:
        if key in self.cache:
            self.list.remove(self.cache.pop(key))
        if len(self.cache) == self.capacity:
            last = self.list.last()
            self.list.remove(last)
            self.cache.pop(last.key)
        node = Node(key, value)
        self.list.insert(node)
        self.cache[key] = node