lru_cache.py

class ListNode:
    def __init__(self, key, value):
        self.key = key
        self.value = value

        self.prev = None
        self.next = None

class LRUCache:
    def __init__(self, capacity):
        self.mapping = {}
        self.cap = capacity

        self.head = ListNode(-1, -1)
        self.tail = ListNode(-1, -1)

        self.head.next = self.tail
        self.tail.prev = self.head

    def get(self, key):
        if key not in self.mapping:
            return -1

        node = self.mapping[key]
        self._remove(node)
        self._add(node)

        return node.value

    def put(self, key, value):
        if key in self.mapping:
            old_node = self.mapping[key]
            self._remove(old_node)

        new_node = ListNode(key, value)
        self._add(new_node)
        self.mapping[key] = new_node

        if len(self.mapping) > self.cap:
            lru_node = self.head.next
            self._remove(lru_node)
            del self.mapping[lru_node.key]

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

        last_node.next = node
        node.prev = last_node

        node.next = self.tail
        self.tail.prev = node

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

        prev_node.next = next_node
        next_node.prev = prev_node