London | 26-SDC-March | Zobeir Rigi | Sprint 2 | Implement an LRU cache

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,92 @@
+class Node:
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value
+        self.next = None
+        self.previous = None
+
+
+class DoublyLinkedList:
+    def __init__(self):
+        self.head = None
+        self.tail = None
+
+    def add_to_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 remove(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.next = None
+        node.previous = None
+
+    def move_to_head(self, node):
+        if node == self.head:
+            return
+
+        self.remove(node)
+        self.add_to_head(node)
+
+    def remove_tail(self):
+        if self.tail is None:
+            return None
+
+        node = self.tail
+        self.remove(node)
+
+        return node
+
+
+class LruCache:
+    def __init__(self, limit):
+        if limit <= 0:
+            raise ValueError("Limit must be greater than 0")
+
+        self.limit = limit
+        self.cache = {}
+        self.items = DoublyLinkedList()
+
+    def get(self, key):
+        node = self.cache.get(key)
+
+        if node is None:
+            return None
+
+        self.items.move_to_head(node)
+
+        return node.value
+
+    def set(self, key, value):
+        if key in self.cache:
+            node = self.cache[key]
+            node.value = value
+            self.items.move_to_head(node)
+            return
+
+        node = Node(key, value)
+
+        self.cache[key] = node
+        self.items.add_to_head(node)
+
+        if len(self.cache) > self.limit:
+            old_node = self.items.remove_tail()
+
+            if old_node is not None:
+                del self.cache[old_node.key]