diff --git a/Sprint-2/implement_lru_cache/linked_list.py b/Sprint-2/implement_lru_cache/linked_list.py new file mode 100644 index 00000000..e25d0cf9 --- /dev/null +++ b/Sprint-2/implement_lru_cache/linked_list.py @@ -0,0 +1,45 @@ +class Node: + def __init__(self, value): + self.value = value + self.previous = None + self.next = None + + +class LinkedList: + def __init__(self): + self.head = None + self.tail = None + + def push_head(self, value): + node = Node(value) + node.next = self.head + + if self.head is None: + self.tail = node + else: + self.head.previous = node + + self.head = node + return node + + def pop_tail(self): + if self.tail is None: + return None + + node = self.tail + self.remove(node) + return node.value + + def remove(self, node): + if node.previous is None: + self.head = node.next + else: + node.previous.next = node.next + + if node.next is None: + self.tail = node.previous + else: + node.next.previous = node.previous + + node.previous = None + node.next = None diff --git a/Sprint-2/implement_lru_cache/lru_cache.py b/Sprint-2/implement_lru_cache/lru_cache.py index e69de29b..089f55b4 100644 --- a/Sprint-2/implement_lru_cache/lru_cache.py +++ b/Sprint-2/implement_lru_cache/lru_cache.py @@ -0,0 +1,41 @@ +from linked_list import LinkedList + + +class _CacheEntry: + def __init__(self, key, value): + self.key = key + self.value = value + + +class LruCache: + def __init__(self, limit): + if limit <= 0: + raise ValueError("Limit must be greater than 0") + + self.limit = limit + self.cache = {} + self.order = LinkedList() + + def get(self, key): + node = self.cache.get(key) + if node is None: + return None + + self.order.remove(node) + self.cache[key] = self.order.push_head(node.value) + return node.value.value + + def set(self, key, value): + node = self.cache.get(key) + if node is not None: + node.value.value = value + self.order.remove(node) + self.cache[key] = self.order.push_head(node.value) + return + + entry = _CacheEntry(key, value) + self.cache[key] = self.order.push_head(entry) + + if len(self.cache) > self.limit: + least_recently_used = self.order.pop_tail() + del self.cache[least_recently_used.key] diff --git a/Sprint-2/implement_lru_cache/lru_cache_test.py b/Sprint-2/implement_lru_cache/lru_cache_test.py index d37df018..be1f6517 100644 --- a/Sprint-2/implement_lru_cache/lru_cache_test.py +++ b/Sprint-2/implement_lru_cache/lru_cache_test.py @@ -54,6 +54,18 @@ def test_eviction_order_after_gets(self): self.assertEqual(cache.get("a"), 1) self.assertEqual(cache.get("c"), 3) + def test_setting_existing_key_updates_value_and_recency(self): + cache = LruCache(limit=2) + + cache.set("a", 1) + cache.set("b", 2) + cache.set("a", 3) + cache.set("c", 4) + + self.assertIsNone(cache.get("b")) + self.assertEqual(cache.get("a"), 3) + self.assertEqual(cache.get("c"), 4) + if __name__ == "__main__": unittest.main()