From 506741fbdfacfbf3010559280c2f00c3e580e1f4 Mon Sep 17 00:00:00 2001
From: antpy <antpy@protonmail.com>
Date: Thu, 24 Aug 2017 01:20:03 -0700
Subject: [PATCH] Basic, mildly tested LRU cache.

---
 src/LRUCache.h | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 src/LRUCache.h

diff --git a/src/LRUCache.h b/src/LRUCache.h
new file mode 100644
index 0000000..f101b3b
--- /dev/null
+++ b/src/LRUCache.h
@@ -0,0 +1,60 @@
+#pragma once
+#ifndef CACHE_H
+#define CACHE_H
+
+#include <unordered_map>
+#include <list>
+#include <utility>
+#include <iostream>
+
+template<class K, class V>
+class LRUCache {
+	using Key_list = std::list<std::pair<K, V>>;
+	Key_list key_values;
+	std::unordered_map<K, typename Key_list::iterator> positions;
+	size_t max_values;
+
+	void remove_oldest() {
+		while (positions.size() >= max_values) {
+			positions.erase(key_values.back().first);
+			key_values.pop_back();
+		}
+	}
+
+public:
+	LRUCache(const size_t max_values) : max_values(max_values) {
+	}
+
+	template<class VV>
+	void insert(const K& key, VV&& value) {
+		remove_oldest();
+		key_values.emplace_front(key, value);
+		positions[key] = key_values.begin();
+	}
+
+	std::pair<V*, bool> find(const K& key) {
+		auto p = positions.find(key);
+		if (p == positions.end())
+			return {nullptr, false};
+		auto iter = p->second;
+		auto& value = iter->second;
+		// If the iterator is not at the front of the list, move it there.
+		if (iter != key_values.begin()) {
+			key_values.splice(
+					key_values.begin(), 
+					key_values, 
+					iter, 
+					std::next(iter));
+		}
+		positions[key] = key_values.begin();
+		return {&(iter->second), true};
+	}
+
+	void debug_cache() {
+		for (auto& p : key_values) {
+			std::cout << p.first << ":" << p.second << std::endl;
+		}
+	}
+};
+
+#endif