【LRU Cache实现】( List + hashtable | template | LRU )

 自动化测试

template < typename Contain >
//重载提取操作符<<
inline std::ostream&
operator<<( std::ostream& o, const std::optional< Contain >& object ){
	using namespace std::literals::string_literals;
	if( !object ) // optional< T >::operator bool()隐式转换
		return ( o << "null"s ); //cache未命中
	return ( o << object.value() );        //cache命中
}
//自动化测试
int main( void ){
	LURCache< std::ptrdiff_t, int > cache;
	//cache default capacity == 64
	int counter { 32 };
	//读写操作总次数
	srand( ( unsigned)time( nullptr ) );
	//随机数种子
	while( counter-- ){
		if( rand() % 101 <= 80  ){
		//80% load写操作
			int key { rand() % 64 };
			int value { rand() % 64 };
			std::printf("#put {key : %d, value: %d}...\n\n", key, value );
			cache.put({key,value});
		}else{
		//20% 读操作
			int key { rand() %64 };
			std::printf("#try-get {key: %d, value : ?}...\n\n", key );
			std::cout << "value:\t" << cache.get(key) << '\n';
		}
	}
	return 0;
}

运行结果

 

LRUCache实现

#include 
#include 
#include 
#include 
#include 
#include 

template < class Key, class Value >
	requires requires{
		std::hash< Key >{}( std::declval< Key >() );
	}
class LURCache{
public:
	static constexpr std::size_t DEFAULT { 64 };
private:
	std::list< Key > cache;
	mutable std::unordered_map< Key, Value > hash;
	std::size_t capacity { DEFAULT };
public:
	typedef Key key_type;
	typedef Value value_type;
	typedef std::pair< Key, Value > pair_type;
	typedef std::optional< Value > return_type;
	LURCache( void ) noexcept = default;
	LURCache( const LURCache& ) noexcept = default;
	LURCache( LURCache&& ) noexcept = default;
	LURCache( std::size_t __capacity ) : capacity( __capacity ) { }
	[[discard]] return_type get( const Key& key )  const {
		if( !hash.count( key ) )
			return static_cast< std::optional< Value > >( std::nullopt );
		return return_type{ hash[key] };
	}
	void put( const pair_type& p ){
		auto [key, value] = p;
        if( hash.count(key)){
            hash[key] = value;
            return;
        }
        if(cache.size() == capacity){
            hash.erase(cache.front());
            cache.pop_front();
        }
        hash.insert(p);
        cache.push_back(key);
	}
};
template < typename Contain >
std::ostream& operator<<( std::ostream& o, const std::optional< Contain >& object ){
	using namespace std::literals::string_literals;
	if( !object ) return ( o << "null"s );
	return ( o << object.value() );
}