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Author: assassint2017

LRU Cache/LRU_Cache.cpp

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+// 使用双向链表和哈希表共同实现
+// typedef 如果写在函数外部，作用范围就是本文件
+// 如果写在函数内，作用范围本函数
+// 如果写在类内，且是公有，就可以在类外用className::typename来调用，如果是私有，当然也就不行了
+
+// Runtime: 120 ms, faster than 40.72% of C++ online submissions for LRU Cache.
+// Memory Usage: 40 MB, less than 32.93% of C++ online submissions for LRU Cache.
+
+class LRUCache 
+{
+public:
+    LRUCache(int capacity) 
+    {
+        maxSize = capacity;
+    }
+    
+    int get(int key) 
+    {
+        auto iter = hashmap.find(key);
+        if (iter == hashmap.end())
+        {
+            return -1;
+        }
+        else
+        {
+            update(iter);
+            return iter->second.first;
+        }
+    }
+    
+    void put(int key, int value) 
+    {
+        auto iter = hashmap.find(key);
+        if (iter == hashmap.end())
+        {
+            if (hashmap.size() == maxSize)
+            {
+                int key = queue.back();
+                queue.pop_back();
+                hashmap.erase(key);
+            }
+
+            queue.push_front(key);
+            hashmap.insert(pair<int, pa>(key, pa(value, queue.begin())));
+        }
+        else
+        {
+            iter->second.first = value;
+            update(iter);
+        }
+    }
+private:
+    typedef list<int>::iterator lit;
+    typedef pair<int, lit> pa;
+private:
+    void update(unordered_map<int, pa>::iterator iter)
+    {
+        int key = iter->first;
+
+        queue.erase(iter->second.second);
+
+        queue.push_front(key);
+
+        iter->second.second = queue.begin();
+    }
+private:
+    int maxSize;
+    list<int> queue;
+    unordered_map<int, pa> hashmap;
+};
+
+/**
+ * Your LRUCache object will be instantiated and called as such:
+ * LRUCache* obj = new LRUCache(capacity);
+ * int param_1 = obj->get(key);
+ * obj->put(key,value);
+ */