Manchester | 25-SDC-Nov | Rahwa Haile | Sprint 2 | Implement an LRU cache in Python

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,99 @@
+class Node:
+    """Represents a node in the doubly-linked list."""
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value
+        self.next = None
+        self.previous = None
+
+
+class DoublyLinkedList:
+    """Manages insertion, removal, and reordering of nodes in a doubly-linked list."""
+    def __init__(self):
+        self.head = None
+        self.tail = None
+
+    def add_to_head(self, node):
+        """Add a node to the head of the list."""
+        node.next = None
+        node.previous = None
+
+        if self.head is None:
+            self.head = node
+            self.tail = node
+        else:
+            node.next = self.head
+            self.head.previous = node
+            self.head = node
+
+    def move_to_head(self, node):
+        """Move an existing node to the head of the list."""
+        if node == self.head:
+            return
+
+        self.remove_node(node)
+        self.add_to_head(node)
+
+    def remove_node(self, node):
+        """Remove a node from the list."""
+        if node == self.head == self.tail:
+            self.head = None
+            self.tail = None
+        elif node == self.head:
+            self.head = node.next
+            self.head.previous = None
+        elif node == self.tail:
+            self.tail = node.previous
+            self.tail.next = None
+        else:
+            node.previous.next = node.next
+            node.next.previous = node.previous
+
+        node.next = None
+        node.previous = None
+
+    def get_tail(self):
+        """Return the tail node (least recently used)."""
+        return self.tail
+
+
+class LruCache:
+    """Implements an LRU cache with O(1) operations."""
+    def __init__(self, limit):
+        if limit <= 0:
+            raise ValueError("Cache limit must be greater than 0")
+
+        self.limit = limit
+        self.cache = {}  
+        self.order = DoublyLinkedList()
+
+    def get(self, key):
+        """Retrieve a value and mark it as recently used."""
+        if key not in self.cache:
+            return None
+
+        node = self.cache[key]
+        self.order.move_to_head(node)
+
+        return node.value
+
+    def set(self, key, value):
+        """Store a key-value pair and evict LRU if necessary."""
+        if key in self.cache:
+            node = self.cache[key]
+            node.value = value
+            self.order.move_to_head(node)
+        else:
+            if len(self.cache) >= self.limit:
+                self._evict_lru()
+
+            new_node = Node(key, value)
+            self.cache[key] = new_node
+            self.order.add_to_head(new_node)
+
+    def _evict_lru(self):
+        """Remove the least recently used item."""
+        lru_node = self.order.get_tail()
+        if lru_node is not None:
+            del self.cache[lru_node.key]
+            self.order.remove_node(lru_node)