lru_cache.py

class Node:
    def __init__(self, key, value):
        self.key = key
        self.value = value
        self.next = None
        self.prev = None
    
class LRUCache:
    def __init__(self, capacity: int):
        self.capacity = capacity
        self.cache = {} 

        self.left = Node(0, 0)
        self.right = Node(0, 0)
        self.left.next = self.right
        self.right.prev = self.left
        
    def remove(self, node):
        node.prev.next = node.next
        node.next.prev = node.prev
        
    def add(self, node):
        node.prev = self.right.prev
        node.next =  self.right
        self.right.prev.next = node
        self.right.prev = node
        
        
    def get(self, key: int) -> int:
        if key in self.cache:
            self.remove(self.cache[key])
            self.add(self.cache[key])
            return self.cache[key].value
        return -1

    def put(self, key: int, value: int) -> None:
        if key in self.cache:
            self.remove(self.cache[key])
        self.cache[key] = Node(key, value)
        self.add(self.cache[key])
        
        if len(self.cache) > self.capacity:
            lru = self.left.next
            self.remove(lru)
            del self.cache[lru.key]