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

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,77 @@
+class LruCache:
+    class clsNode:
+        def __init__(self, value, key):
+            self.next = None
+            self.previous = None
+            self.value = value
+            self.key = key
+
+    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 = {}
+
+    def add_to_head(self, node):
+        if node == None:
+            return
+        if self.head is None:
+            self.head = node
+            self.tail = node
+        else:
+            node.next = self.head
+            self.head.previous = node
+            self.head = node
+
+    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
+
+    def move_to_head(self, node):
+        self.remove(node)
+        self.add_to_head(node)
+
+    # cache {key,node}
+    def get(self, key):
+        target = self.cache.get(key)
+        if target == None:
+            return None
+
+        self.move_to_head(target)
+        return target.value
+
+    def set(self, key, value):
+        target = self.cache.get(key)
+
+        if target is not None:
+            target.value = value
+            self.move_to_head(target)
+
+        else:
+            target = self.clsNode(value, key)
+            self.add_to_head(target)
+            self.cache[key] = target
+
+            if len(self.cache) > self.limit:
+                old_tail = self.tail
+                self.remove(old_tail)
+                del self.cache[old_tail.key]