London | 26-SDC-March | Jamal Laqdiem| Sprint 2 | Implement an LRU cache

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,50 @@
+import sys
+import os
+sys.path.append(os.path.abspath(os.path.join(os.path.dirname(__file__), "../implement_linked_list")))
+
+from linked_list import LinkedList, Node # type:ignore
+from typing import Any
+
+class LruCache:
+    def __init__(self, limit: int):
+        if limit <= 0:
+            raise ValueError("Limit must be greater than 0")
+        self.capacity = limit
+        # maps key
+        self.cache: dict[Any, Node] = {} 
+        # tracking the usage order head first tail last.
+        self.list = LinkedList() 
+
+    def get(self, key: Any) -> Any:
+        # If key not exist return None
+        if key not in self.cache:
+            return None
+
+        node_handle = self.cache[key]
+
+        # we get  the value to return
+        _, value = node_handle.value
+
+        # we use remove() and push_head() to remove it from the position to the head
+        self.list.remove(node_handle)
+        self.cache[key] = self.list.push_head((key, value))
+
+        return value
+
+    def set(self, key: Any, value: Any) -> None:
+        if key in self.cache:
+            self.list.remove(self.cache[key])
+            # we do this because the position and value about to change.
+            del self.cache[key]
+
+          # we call pop_tail() to cut off the tail
+        elif len(self.cache) >= self.capacity:
+            # return the value stored in the tail node
+            oldest_item = self.list.pop_tail()
+            if oldest_item:
+                oldest_key, _ = oldest_item
+                del self.cache[oldest_key]
+
+        ## place the new items at the head of stack and update and return the object Node.
+        new_node = self.list.push_head((key, value))
+        self.cache[key] = new_node