West Midlands | 25-SDC-July | Gabriel Deng | Sprint 2 | Implement and LRU cache in Python

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,73 @@
+class Node:
+    """Represents a single node in the doubly linked list."""
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value
+        self.prev = None
+        self.next = None
+
+
+class DoublyLinkedList:
+    """Manages a doubly linked list with sentinel head and tail nodes."""
+
+    def __init__(self):
+        self.head = Node(None, None)
+        self.tail = Node(None, None)
+        self.head.next = self.tail
+        self.tail.prev = self.head
+
+    def add_to_front(self, node):
+        """Add a node to the front of the list (right after head)."""
+        node.prev = self.head
+        node.next = self.head.next
+        self.head.next.prev = node
+        self.head.next = node
+
+    def remove(self, node):
+        """Remove a node from the list."""
+        prev_node = node.prev
+        next_node = node.next
+        prev_node.next = next_node
+        next_node.prev = prev_node
+
+    def get_least_recent(self):
+        """Get the least recently used node (just before tail)."""
+        return self.tail.prev
+
+
+class LruCache:
+    """LRU Cache implementation using a doubly linked list to track usage order."""
+
+    def __init__(self, limit):
+        if limit <= 0:
+            raise ValueError("Capacity must be greater than 0")
+        self.capacity = limit
+        self.cache = {}
+        self.linked_list = DoublyLinkedList()
+
+    def get(self, key):
+        """Get a value from the cache and mark it as recently used."""
+        if key not in self.cache:
+            return None
+
+        node = self.cache[key]
+        self.linked_list.remove(node)
+        self.linked_list.add_to_front(node)
+        return node.value
+
+    def set(self, key, value):
+        """Set a value in the cache, evicting the LRU item if at capacity."""
+        if key in self.cache:
+            node = self.cache[key]
+            node.value = value
+            self.linked_list.remove(node)
+            self.linked_list.add_to_front(node)
+        else:
+            new_node = Node(key, value)
+            self.cache[key] = new_node
+            self.linked_list.add_to_front(new_node)
+
+            if len(self.cache) > self.capacity:
+                lru = self.linked_list.get_least_recent()
+                self.linked_list.remove(lru)
+                del self.cache[lru.key]