LRU Cache

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

class LRUCache:
    def __init__(self, capacity):
        self.capacity = capacity
        self.cache = {}
        self.head = Node(0, 0)
        self.tail = Node(0, 0)
        self.head.next = self.tail
        self.tail.prev = self.head

    def _remove(self, node):
        node.prev.next = node.next
        node.next.prev = node.prev

    def _add_to_front(self, node):
        node.prev = self.head
        node.next = self.head.next
        self.head.next.prev = node
        self.head.next = node

    def get(self, key):
        if key in self.cache:
            node = self.cache[key]
            self._remove(node)
            self._add_to_front(node)
            return node.value
        return -1

    def put(self, key, value):
        if key in self.cache:
            node = self.cache[key]
            self._remove(node)
            del self.cache[key]

        self.cache[key] = Node(key, value)
        self._add_to_front(self.cache[key])
        
        if len(self.cache) > self.capacity:
            lru_node = self.tail.prev
            self._remove(lru_node)
            del self.cache[lru_node.key]