New changes for SRP

Author: gai93003

Sprint-2/implement_lru_cache/lru_cache.py

@@ -1,57 +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 LruCache:
-    def __init__(self, limit):
-        if limit <= 0:
-            raise ValueError("Capacity must be greater than 0")
-        self.capacity = limit
-        self.cache = {}
-
+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 _remove(self, node):
+    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 _add_to_front(self, node):
-        node.prev = self.head
-        node.next = self.head.next
-        self.head.next.prev = node
-        self.head.next = 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._remove(node)
-        self._add_to_front(node)
+        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._remove(node)
-            self._add_to_front(node)
+            self.linked_list.remove(node)
+            self.linked_list.add_to_front(node)
         else:
             new_node = Node(key, value)
             self.cache[key] = new_node
-            self._add_to_front(new_node)
+            self.linked_list.add_to_front(new_node)
 
             if len(self.cache) > self.capacity:
-                lru = self.tail.prev
-                self._remove(lru)
+                lru = self.linked_list.get_least_recent()
+                self.linked_list.remove(lru)
                 del self.cache[lru.key]