Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set. get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1. set(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.

from collections import OrderedDict
class LRUCache:
    def __init__(self, capacity: int):
        self.cache = OrderedDict()
        self.capacity = capacity
    def get(self, key: int) -> int:
        if key in self.cache:
            self.cache.move_to_end(key)
            return self.cache[key]
        else:
            return -1
    def put(self, key: int, value: int) -> None:
        if key in self.cache:
            del self.cache[key]
        self.cache[key] = value
        if len(self.cache) > self.capacity:
            self.cache.popitem(last=False)

class Node:
    def __init__(self, key, val):
        self.key = key
        self.val = val
        self.prev = 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 get(self, key):
        if key not in self.cache:
            return -1
        node = self.cache[key]
        self._remove(node)
        self._add(node)
        return node.val

    def put(self, key, value):
        if key in self.cache:
            self._remove(self.cache[key])
        node = Node(key, value)
        self._add(node)
        self.cache[key] = node
        if len(self.cache) > self.capacity:
            del self.cache[self.head.next.key]
            self._remove(self.head.next)

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

    def _add(self, node):
        p = self.tail.prev
        p.next = node
        node.next = self.tail
        self.tail.prev = node
        node.prev = p