first hard problem

Author: shangchun

lruCache.py

@@ -0,0 +1,103 @@
+# Hash + Link List
+# @link http://www.acmerblog.com/leetcode-lru-cache-lru-5745.html
+
+class Node:
+    def __init__(self, key, val):
+        self.key = key
+        self.val = val
+        self.previous = None
+        self.next = None
+
+class LRUCache:
+
+    # @param capacity, an integer
+    def __init__(self, capacity):
+        self.capacity = capacity
+        self.count = 0
+        self.cache = {}
+        self.head = Node(None, None)
+        self.tail = Node(None, None)
+        self.head.next = self.tail
+        self.tail.previous = self.head
+
+    def attach(self, node):
+        self.head.next.previous = node
+        node.next = self.head.next
+        self.head.next = node
+        node.previous = self.head
+
+    def detach(self, node):
+        node.previous.next = node.next
+        node.next.previous = node.previous
+
+    # @return an integer
+    def get(self, key):
+        if key in self.cache:
+            node = self.cache[key]
+            self.detach(node)
+            self.attach(node)
+            return node.val
+        else:
+            return -1
+
+    # @param key, an integer
+    # @param value, an integer
+    # @return nothing
+    def set(self, key, value):
+        if key in self.cache:
+            oldNode = self.cache[key]
+            node = Node(key, value)
+            self.cache[key] = node
+            self.detach(oldNode)
+            self.attach(node)
+        else:
+            if self.count == self.capacity:
+                node = self.tail.previous
+                self.detach(node)
+                del self.cache[node.key]
+                del node
+                self.count -= 1
+            self.count += 1
+            node = Node(key, value)
+            self.cache[key] = node
+            self.attach(node)
+
+c1 = LRUCache(2)
+c1.set(1, 2)
+c1.set(2, 4)
+assert c1.get(2) == 4
+assert c1.get(1) == 2
+c1.set(3, 6)
+assert c1.get(2) == -1
+assert c1.get(3) == 6
+
+c2 = LRUCache(1)
+c2.set(2, 1)
+assert c2.get(2) == 1
+c2.set(3, 2)
+assert c2.get(2) == -1
+assert c2.get(3) == 2
+
+c3 = LRUCache(2)
+c3.set(2,1)
+c3.set(2,2)
+assert c3.get(2) == 2
+c3.set(1,1)
+c3.set(4,1)
+assert c3.get(2) == -1
+
+c4 = LRUCache(3)
+c4.set(1,1)
+c4.set(2,2)
+c4.set(3,3)
+c4.set(4,4)
+c4.get(4)
+c4.get(3)
+c4.get(2)
+c4.get(1)
+c4.set(5,5)
+c4.get(1)
+c4.get(2)
+c4.get(3)
+assert c4.get(4) == -1
+c4.get(5)