Glasgow | 26-SDC-Mar | Mohammed Abdoon | Sprint 2 | Implement an LRU cache

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,78 @@
+class _Node:
+    __slots__ = ('key', 'value', 'previous', 'next')
+
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value
+        self.previous = None
+        self.next = None
+
+
+class LruCache:
+    def __init__(self, limit):
+        if limit <= 0:
+            raise ValueError('limit must be greater than zero')
+        self.limit = limit
+        self.map = {}
+        self.head = None
+        self.tail = None
+        self.size = 0
+
+    def _unlink(self, node):
+        if node.previous is not None:
+            node.previous.next = node.next
+        else:
+            self.head = node.next
+
+        if node.next is not None:
+            node.next.previous = node.previous
+        else:
+            self.tail = node.previous
+
+        node.previous = None
+        node.next = None
+
+    def _link_head(self, node):
+        node.previous = None
+        node.next = self.head
+        if self.head is not None:
+            self.head.previous = node
+        self.head = node
+        if self.tail is None:
+            self.tail = node
+
+    def _move_to_head(self, node):
+        if node is self.head:
+            return
+        self._unlink(node)
+        self._link_head(node)
+
+    def _evict_tail(self):
+        if self.tail is None:
+            return
+        node = self.tail
+        self._unlink(node)
+        del self.map[node.key]
+        self.size -= 1
+
+    def set(self, key, value):
+        if key in self.map:
+            node = self.map[key]
+            node.value = value
+            self._move_to_head(node)
+            return
+
+        node = _Node(key, value)
+        self.map[key] = node
+        self._link_head(node)
+        self.size += 1
+
+        if self.size > self.limit:
+            self._evict_tail()
+
+    def get(self, key):
+        node = self.map.get(key)
+        if node is None:
+            return None
+        self._move_to_head(node)
+        return node.value