London | 25-SDC-NOV | Jesus del Moral | Sprint 2 | LRU Cache

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,82 @@
+class Node:
+    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 positive")
+
+        self.limit = limit
+        self.cache = {}  # key -> node
+        self.head = None  # Most recently used
+        self.tail = None  # Least recently used
+
+    # ---------------------
+    # Internal helpers
+    # ---------------------
+
+    def _remove_node(self, node):
+        if node.previous:
+            node.previous.next = node.next
+        else:
+            self.head = node.next
+
+        if node.next:
+            node.next.previous = node.previous
+        else:
+            self.tail = node.previous
+
+        node.previous = None
+        node.next = None
+
+    def _add_to_head(self, node):
+        node.next = self.head
+        node.previous = None
+
+        if self.head:
+            self.head.previous = node
+        else:
+            self.tail = node
+
+        self.head = node
+
+    # ---------------------
+    # Public API
+    # ---------------------
+
+    def get(self, key):
+        node = self.cache.get(key)
+        if not node:
+            return None
+
+        # Move to head (recently used)
+        self._remove_node(node)
+        self._add_to_head(node)
+
+        return node.value
+
+    def set(self, key, value):
+        node = self.cache.get(key)
+
+        if node:
+            # Update value and move to head
+            node.value = value
+            self._remove_node(node)
+            self._add_to_head(node)
+            return
+
+        # If full, evict LRU (tail)
+        if len(self.cache) >= self.limit:
+            lru = self.tail
+            self._remove_node(lru)
+            del self.cache[lru.key]
+
+        # Insert new node
+        new_node = Node(key, value)
+        self._add_to_head(new_node)
+        self.cache[key] = new_node

Sprint-2/implement_lru_cache/lru_cache_test.py

@@ -1,5 +1,4 @@
 import unittest
-
 from lru_cache import LruCache
 
 class LruCacheTest(unittest.TestCase):