Refactor LRU cache to use OrderedDict

Author: shreefAhmedM

Sprint-2/implement_lru_cache/lru_cache.py

@@ -1,10 +1,5 @@
 
-class _Node:
-    def __init__(self, key=None, value=None):
-        self.key = key
-        self.value = value
-        self.prev = None
-        self.next = None
+from collections import OrderedDict
 
 
 class LruCache:
@@ -13,50 +8,22 @@ def __init__(self, limit):
             raise ValueError("limit must be greater than zero")
 
         self.limit = limit
-        self.cache = {}
-        self.head = _Node()
-        self.tail = _Node()
-
-        self.head.next = self.tail
-        self.tail.prev = self.head
-
-    def _remove(self, node):
-        node.prev.next = node.next
-        node.next.prev = node.prev
-
-    def _add_to_front(self, node):
-        node.prev = self.head
-        node.next = self.head.next
-
-        self.head.next.prev = node
-        self.head.next = node
-
-    def _mark_as_used(self, node):
-        self._remove(node)
-        self._add_to_front(node)
+        self.cache = OrderedDict()
 
     def get(self, key):
-        node = self.cache.get(key)
-
-        if node is None:
+        if key not in self.cache:
             return None
 
-        self._mark_as_used(node)
-        return node.value
+        self.cache.move_to_end(key)
+        return self.cache[key]
 
     def set(self, key, value):
-        node = self.cache.get(key)
-
-        if node is not None:
-            node.value = value
-            self._mark_as_used(node)
+        if key in self.cache:
+            self.cache[key] = value
+            self.cache.move_to_end(key)
             return
 
-        node = _Node(key, value)
-        self.cache[key] = node
-        self._add_to_front(node)
+        self.cache[key] = value
 
         if len(self.cache) > self.limit:
-            lru_node = self.tail.prev
-            self._remove(lru_node)
-            del self.cache[lru_node.key]
+            self.cache.popitem(last=False)