Create lru_cache.py

Author: peijunz

Diff for: lru_cache.py

@@ -0,0 +1,59 @@
+from dataclasses import dataclass 
+
+@dataclass
+class ListNode:
+    key: any
+    val: any
+    prev: 'ListNode'
+    next: 'ListNode'
+
+class LinkedList:
+    def __init__(self):
+        self.head = ListNode(None, None, None, None)
+        self.head.prev = self.head.next = self.head # null.next should be the most recent
+    
+    def insert(self, node):
+        next_node = self.head.next
+        self.head.next, node.next = node, next_node
+        node.prev, next_node.prev = self.head, node
+    
+    def extract(self, node):
+        # print(node.val)
+        assert node != self.head
+        prev, next = node.prev, node.next
+        prev.next, next.prev = next, prev
+        node.prev = node.next = None
+        return node
+
+class LRUCache:
+    def __init__(self, capacity: int):
+        self.capacity = capacity
+        self.cnt = 0
+        self.nodemap = {}
+        self.linkedlist = LinkedList()
+
+    def get(self, key: int) -> int:
+        if key in self.nodemap:
+            node = self.nodemap.get(key)
+            self.linkedlist.extract(node)
+            self.linkedlist.insert(node)
+            return node.val
+        else:
+            return -1
+
+    def put(self, key: int, value: int) -> None:
+        if key in self.nodemap:
+            node = self.nodemap.get(key)
+            self.linkedlist.extract(node)
+            self.linkedlist.insert(node)
+            node.val = value
+        else:
+            if self.cnt == self.capacity:
+                lru_node = self.linkedlist.head.prev
+                self.linkedlist.extract(lru_node)
+                del self.nodemap[lru_node.key]
+                self.cnt -= 1
+            node = ListNode(key, value, None, None)
+            self.nodemap[key] = node
+            self.linkedlist.insert(node)
+            self.cnt += 1