Added Code for LRU Cache

LRU Cache/LRUCache.cpp

@@ -0,0 +1,43 @@
+class LRUCache {
+public:
+    LRUCache(int capacity) {
+        this->capacity = capacity;
+    }
+
+    int get(int key) {
+        if(cache.find(key) != cache.end())
+        {
+            use(key);
+            return cache[key];
+        }
+        return -1;
+    }
+
+    void put(int key, int value) {
+        use(key);
+        cache[key] = value;
+    }
+
+private:
+    int capacity;
+    list<int> recent;
+    unordered_map<int,int> cache;
+    unordered_map<int, list<int>::iterator> pos;
+
+    void use(int key)
+    {
+        if(pos.find(key) != pos.end())
+        {
+            recent.erase(pos[key]);
+        }
+        else if(recent.size() >= capacity)
+        {
+            int old = recent.back();
+            recent.pop_back();
+            cache.erase(old);
+            pos.erase(old);
+        }
+        recent.push_front(key);
+        pos[key] = recent.begin();
+    }
+};