From 71f6fc9baff6fd4228f7dc70aced72143db31224 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Sun, 8 Nov 2020 16:19:37 +0300
Subject: [PATCH] Add LRU cache implementation

---
 libs/util/include/psemek/util/lru_cache.hpp | 59 +++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 libs/util/include/psemek/util/lru_cache.hpp

diff --git a/libs/util/include/psemek/util/lru_cache.hpp b/libs/util/include/psemek/util/lru_cache.hpp
new file mode 100644
index 00000000..2acecb47
--- /dev/null
+++ b/libs/util/include/psemek/util/lru_cache.hpp
@@ -0,0 +1,59 @@
+#pragma once
+
+#include <list>
+#include <unordered_map>
+
+namespace psemek::util
+{
+
+	template <typename T>
+	struct lru_cache
+	{
+		bool empty() const;
+		std::size_t count(T const & value) const;
+
+		T pop();
+		void push(T value);
+
+	private:
+		std::list<T> queue_;
+		std::unordered_map<T, typename std::list<T>::iterator> queue_it_map_;
+	};
+
+	template <typename T>
+	bool lru_cache<T>::empty() const
+	{
+		return queue_.empty();
+	}
+
+	template <typename T>
+	std::size_t lru_cache<T>::count(T const & value) const
+	{
+		return queue_it_map_.count(value);
+	}
+
+	template <typename T>
+	T lru_cache<T>::pop()
+	{
+		auto value = std::move(queue_.front());
+		queue_.pop_front();
+		queue_it_map_.erase(value);
+		return value;
+	}
+
+	template <typename T>
+	void lru_cache<T>::push(T value)
+	{
+		auto it = queue_it_map_.find(value);
+		if (it == queue_it_map_.end())
+		{
+			queue_.push_back(value);
+			queue_it_map_[std::move(value)] = queue_.back();
+		}
+		else
+		{
+			queue_.splice(queue_.begin(), queue_, *it);
+		}
+	}
+
+}