LRUCacheGeneric.cs

namespace Library;

public class LRUCache<K,V>
{
    private object _syncRoot =new object();

    private readonly Dictionary<K, LinkedListNode<KeyValuePair<K,V>>> _dictionary;
    private readonly LinkedList<KeyValuePair<K,V>> _linkedList;
    private readonly int _boundedCapacity;

    public LRUCache(int boundedCapacity)
    {

        if (boundedCapacity < 0)
            throw new ArgumentOutOfRangeException(nameof(boundedCapacity));
        _dictionary = new(boundedCapacity + 1);
        _linkedList = new();
        _boundedCapacity = boundedCapacity;
    }


    public int Count
    {
        get
        {
            lock (_syncRoot) return _dictionary.Count;
        }
    }

    public V Get(K key)
    {
        V retVal = default(V);
        lock (_syncRoot)
        {
            if (_dictionary.TryGetValue(key, out var refNode))
            {
                retVal = refNode.Value.Value;
                if (!ReferenceEquals(refNode, _linkedList.Last))
                {
                    _linkedList.Remove(refNode);
                    _linkedList.AddLast(refNode);
                }
            }
        }

        return retVal;
    }

    public void Put(K key, V value)
    {
        lock (_syncRoot)
        {
            if (_dictionary.TryGetValue(key, out var refNode ))
            {
                refNode.Value = new KeyValuePair<K, V>(key, value);
                if (!ReferenceEquals(refNode, _linkedList.Last))
                {
                    _linkedList.Remove(refNode);
                    _linkedList.AddLast(refNode);
                }
            }
            else
            {
                refNode = new LinkedListNode<KeyValuePair<K,V>>(new KeyValuePair<K, V>(key, value));
                _linkedList.AddLast(refNode);
                _dictionary.Add(key,refNode);
                if (_dictionary.Count > _boundedCapacity)
                {
                    _ = _dictionary.Remove(_linkedList.First!.Value.Key);
                    _linkedList.RemoveFirst();
                }
            }
        }
    }
}