cache_lru.py

from typing import TypeVar, Generic, Optional, Hashable, TypeAlias
from icecream import ic  # type: ignore


KeyT = TypeVar("KeyT", bound=Hashable)
ValueT = TypeVar("ValueT")


class Node(Generic[KeyT, ValueT]):
    def __init__(self, key: Optional[KeyT], value: Optional[ValueT]):
        assert key is not None
        assert value is not None
        self.key: KeyT = key
        self.value: ValueT = value
        self.prev: Node[KeyT, ValueT]
        self.next: Node[KeyT, ValueT]


class List(Generic[KeyT, ValueT]):
    def __init__(self):
        self.head: Node[KeyT, ValueT] = Node[KeyT, ValueT](None, None)
        self.tail: Node[KeyT, ValueT] = Node[KeyT, ValueT](None, None)
        self.head.next = self.tail
        self.tail.prev = self.head

    def push_front(self, node: Node[KeyT, ValueT]) -> None:
        node.prev = self.head
        node.next = self.head.next
        self.head.next.prev = node
        self.head.next = node

    def remove(self, node: Node[KeyT, ValueT] | None) -> None:
        if not node: return
        prev = node.prev
        next = node.next
        prev.next = next
        next.prev = prev

    def move_front(self, node: Node[KeyT, ValueT] | None) -> None:
        if not node: return
        self.remove(node)
        self.push_front(node)

    def back(self) -> Node[KeyT, ValueT] | None:
        if self.tail == self.head: return None
        return self.tail.prev


class LRUCache(Generic[KeyT, ValueT]):
    def __init__(self, capacity: int):
        self.capacity: int = capacity
        self.cache: dict[KeyT, Node[KeyT, ValueT]] = {}
        self.list: List[KeyT, ValueT] = List[KeyT, ValueT]()

    def get(self, key: KeyT) -> ValueT | None:
        node = self.cache.get(key, None)
        if not node:
            return None

        self.list.move_front(node)
        return node.value

    def put(self, key: KeyT, value: ValueT) -> None:
        node = self.cache.get(key)
        if node:
            node.value = value
            self.list.move_front(node)
            return

        if len(self.cache) == self.capacity:
            tail = self.list.back()
            if tail:
                self.list.remove(tail)
                del self.cache[tail.key]

        newNode = Node[KeyT, ValueT](key, value)
        self.cache[key] = newNode
        self.list.push_front(newNode)


if __name__ == '__main__':
    cache = LRUCache[str, str](2)

    cache.put("Response1", "Content1")
    cache.put("Response2", "Content2")  # Response1, Response2
    ic(cache.get("Response1"))  # Content1

    cache.put("Response3", "Content3")  # Response3, Response1
    ic(cache.get("Response2"))  # nil

    cache.put("Response4", "Content4")  # Response4, Response3

    ic(cache.get("Response1"))  # nil
    ic(cache.get("Response2"))  # nil
    ic(cache.get("Response3"))  # Content3
    ic(cache.get("Response4"))  # Content4