London | 26-Jul-SDC | Shaghayegh far| Sprint 2 | Implement LRU Cache

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,70 @@
+
+class Node:
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value
+        self.previous = None
+        self.next = None
+
+
+class DoublyLinkedList:
+    def __init__(self):
+        self.head = Node(None, None)
+        self.tail = Node(None, None)
+
+        self.head.next = self.tail
+        self.tail.previous = self.head
+
+    def add_to_front(self, node):
+        node.next = self.head.next
+        node.previous = self.head
+
+        self.head.next.previous = node
+        self.head.next = node
+
+    def remove(self, node):
+        node.previous.next = node.next
+        node.next.previous = node.previous
+
+    def remove_last(self):
+        node = self.tail.previous
+        self.remove(node)
+        return node
+
+
+class LruCache:
+    def __init__(self, limit):
+        if limit <= 0:
+            raise ValueError("Limit must be greater than zero")
+
+        self.limit = limit
+        self.cache = {}
+        self.order = DoublyLinkedList()
+
+    def get(self, key):
+        if key not in self.cache:
+            return None
+
+        node = self.cache[key]
+
+        self.order.remove(node)
+        self.order.add_to_front(node)
+
+        return node.value
+
+    def set(self, key, value):
+        if key in self.cache:
+            node = self.cache[key]
+            node.value = value
+
+            self.order.remove(node)
+            self.order.add_to_front(node)
+            return
+
+        if len(self.cache) >= self.limit:
+            oldest_node = self.order.remove_last()
+            del self.cache[oldest_node.key]
+
+        new_node = Node(key, value)
+        self.cache[key] = new_node
+        self.order.add_to_front(new_node)