NW| 26-Jul-SDC | Ahmad Hmedan | Sprint 2 | Implement an LRU cache in Python

Sprint-2/implement_lru_cache/linked_list.py

@@ -0,0 +1,56 @@
+class LinkedList:
+    class Node:
+        __slots__ = ("next","previous","value")
+
+        def __init__(self, value):
+            self.next = None
+            self.previous = None
+            self.value = value
+
+    def __init__(self):
+        self.head = None
+        self.tail = None
+        self.size = 0
+
+    def push_head(self, value):
+        new_node = self.Node(value=value)
+        if self.head == None:
+            self.head = new_node
+            self.tail = new_node
+        else:
+            new_node.next = self.head
+            self.head.previous = new_node
+            self.head = new_node
+        self.size += 1
+        return new_node
+
+    def pop_tail(self):
+        if self.tail == None:
+            return
+        removed_value = self.tail.value
+
+        self.remove(self.tail)
+        return removed_value
+
+
+    def remove(self, node):
+        if node == None:
+            return
+        if node == self.head and node == self.tail:
+            self.head = None
+            self.tail = None
+
+        elif node == self.head:
+            self.head = self.head.next
+            self.head.previous = None
+
+        elif node == self.tail:
+            self.tail = self.tail.previous
+            self.tail.next = None
+
+        else:
+            node.next.previous = node.previous
+            node.previous.next = node.next
+        node.next = None
+        node.previous = None
+        self.size -= 1

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,49 @@
+from linked_list import LinkedList
+
+
+class LruCache:
+
+    def __init__(self, limit):
+        if limit <= 0:
+            raise ValueError("limit must be greater than 0")
+        # self.head = None
+        # self.tail = None
+        # self.limit = limit
+        # self.cache = {}
+        self.list = LinkedList()
+        self.limit = limit
+        self.cache = {}
+
+    def move_to_head(self, node):
+
+        key, value = node.value
+
+        self.list.remove(node)
+        new_node = self.list.push_head((key, value))
+        self.cache[key] = new_node
+
+    def get(self, key):
+        target = self.cache.get(key)
+        if target == None:
+            return None
+
+        self.move_to_head(target)
+
+        return target.value[1]
+
+    def set(self, key, value):
+        target = self.cache.get(key)
+
+        if target is not None:
+
+            target.value = (key, value)
+            self.move_to_head(target)
+
+        else:
+
+            new_Node = self.list.push_head((key, value))
+            self.cache[key] = new_Node
+
+            if len(self.cache) > self.limit:
+                old_key, old_value = self.list.pop_tail()
+                del self.cache[old_key]