LRU Cache — LeetCode 146 Python Solution

class Node:
    def __init__(self, key: int = 0, val: int = 0):
        self.key = key
        self.val = val
        self.prev = None
        self.next = None


class LRUCache:

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

    def get(self, key: int) -> int:
        if key not in self.cache:
            return -1
        node = self.cache[key]
        self.remove_node(node)
        self.add_to_head(node)
        return node.val

    def put(self, key: int, value: int) -> None:
        if key in self.cache:
            node = self.cache[key]
            self.remove_node(node)
            node.val = value
            self.add_to_head(node)
        else:
            node = Node(key, value)
            self.cache[key] = node
            self.add_to_head(node)
            self.size += 1
            if self.size > self.capacity:
                node = self.tail.prev
                self.cache.pop(node.key)
                self.remove_node(node)
                self.size -= 1

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

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


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