Added LRU Cache

other/lru_cache.py

@@ -0,0 +1,127 @@
+class Double_Linked_List_Node():
+    '''
+    Double Linked List Node built specifically for LRU Cache
+    '''
+
+    def __init__(self, key, val):
+        self.key = key
+        self.val = val
+        self.next = None
+        self.prev = None
+
+
+class Double_Linked_List():
+    '''
+    Double Linked List built specifically for LRU Cache
+    '''
+
+    def __init__(self):
+        self.head = Double_Linked_List_Node(None, None)
+        self.rear = Double_Linked_List_Node(None, None)
+        self.head.next, self.rear.prev = self.rear, self.head
+
+    def add(self, node: Double_Linked_List_Node) -> None:
+        '''
+        Adds the given node to the end of the list (before rear)
+        '''
+        temp = self.rear.prev
+        temp.next, node.prev = node, temp
+        self.rear.prev, node.next = node, self.rear
+
+    def remove(self, node: Double_Linked_List_Node) -> Double_Linked_List_Node:
+        '''
+        Removes and returns the given node from the list
+        '''
+        temp_last, temp_next = node.prev, node.next
+        node.prev, node.next = None, None
+        temp_last.next, temp_next.prev = temp_next, temp_last
+
+        return node
+
+
+class Lru_Cache:
+    '''
+    LRU Cache to store a given capacity of data
+
+    >>> cache = Lru_Cache(2)
+
+    >>> cache.set(1, 1)
+
+    >>> cache.set(2, 2)
+
+    >>> cache.get(1)
+    1
+
+    >>> cache.set(3, 3)
+
+    >>> cache.get(2)
+    Traceback (most recent call last):
+    ...
+    ValueError: Key '2' not found in cache
+
+    >>> cache.set(4, 4)
+
+    >>> cache.get(1)
+    Traceback (most recent call last):
+    ...
+    ValueError: Key '1' not found in cache
+
+    >>> cache.get(3)
+    3
+
+    >>> cache.get(4)
+    4
+
+    >>> cache.has_key(1)
+    False
+
+    >>> cache.has_key(4)
+    True
+    '''
+
+    def __init__(self, capacity):
+        self.list = Double_Linked_List()
+        self.capacity = capacity
+        self.num_keys = 0
+        self.cache = {}
+
+    def get(self, key: int) -> int:
+        '''
+        Returns the value for the input key and updates the Double Linked List. Raises
+        Value Error if key is not present in cache
+        '''
+        if key in self.cache:
+            self.list.add(self.list.remove(self.cache[key]))
+            return self.cache[key].val
+        raise ValueError(f"Key '{key}' not found in cache")
+
+    def set(self, key: int, value: int) -> None:
+        '''
+        Sets the value for the input key and updates the Double Linked List
+        '''
+        if key not in self.cache:
+            if self.num_keys >= self.capacity:
+                key_to_delete = self.list.head.next.key
+                self.list.remove(self.cache[key_to_delete])
+                del self.cache[key_to_delete]
+                self.num_keys -= 1
+            self.cache[key] = Double_Linked_List_Node(key, value)
+            self.list.add(self.cache[key])
+            self.num_keys += 1
+
+        else:
+            node = self.list.remove(self.cache[key])
+            node.val = value
+            self.list.add(node)
+
+    def has_key(self, key: int) -> bool:
+        '''
+        Checks if the input key is present in cache
+        '''
+        return key in self.cache
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()