London | 25-SDC-Nov | Emiliano Uruena | Sprint 2 | LRU-cache Python

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,91 @@
+
+class Node:
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value      
+        self.previous = None        
+        self.next = None       
+class LinkedList:
+    def __init__(self):
+        self.head = None        
+        self.tail = None        
+
+    # adding a new value in the front of the list
+    def push_head(self, node):
+        node.previous = None
+        node.next = self.head      
+
+        if self.head is None:   # if list is empty head and tail becomes this node.
+            self.head = node    
+            self.tail = node    
+        else:
+            self.head.previous = node   
+            self.head = node        
+
+        return node  # returns the node so we can remove it later
+
+    # removing last element
+    def pop_tail(self):
+        if self.tail is None:   
+            raise Exception("List is empty")
+
+        removed = self.tail 
+        self.remove(removed)
+        return removed
+
+    # removes a specific node 
+    def remove(self, node):
+
+        if node.previous is None:   # if removing head
+            self.head = node.next
+        else:
+            node.previous.next = node.next  # connect previous to next
+
+        if node.next is None:   # if removing tail
+            self.tail = node.previous
+        else:
+            node.next.previous = node.previous  # connect next to previous
+    # unplugging node
+        node.next = None
+        node.previous = None
+
+class LruCache:
+    def __init__(self,limit) -> None:
+        if limit <= 0:
+            raise ValueError("Limit must be greater than zero")
+        self.limit = limit
+
+        self.storage =  {} 
+        self.order = LinkedList()
+        pass
+
+    #If key already exists move it to MRU
+    def touch (self,node):
+        self.order.remove(node)
+        self.order.push_head(node)
+
+    # If we want to add or update a key value pair
+    def set(self, key, value):
+        if key in self.storage:
+            node = self.storage[key]   #update the value of the key 
+            node.value = value
+            self.touch(node)
+            return
+
+        #if we are adding a new key and at our limit 
+        if len(self.storage) >= self.limit:
+            lru_node =self.order.pop_tail()
+            del self.storage[lru_node.key]
+
+        #insert a new node
+        new_node = Node(key, value)
+        self.order.push_head(new_node)
+        self.storage[key] = new_node
+
+    # updating position to most recently used 
+    def get(self,key):
+        if key not in self.storage:
+            return None
+        node = self.storage[key]
+        self.touch(node)
+        return node.value