LRUCacheIntPairs.cs

namespace Library;
using IntPair = KeyValuePair<int, int>;
public class LRUCache
{
    private object _syncRoot =new object();

    private readonly Dictionary<int, LinkedListNode<IntPair>> _dictionary;
    private readonly LinkedList<IntPair> _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 int Get(int key)
    {
        int retVal = -1;
        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(int key, int value)
    {
        lock (_syncRoot)
        {
            if (_dictionary.TryGetValue(key, out var refNode ))
            {
                refNode.Value = new IntPair(key, value);
                if (!ReferenceEquals(refNode, _linkedList.Last))
                {
                    _linkedList.Remove(refNode);
                    _linkedList.AddLast(refNode);
                }
            }
            else
            {
                refNode = new LinkedListNode<IntPair>(new IntPair(key, value));
                _linkedList.AddLast(refNode);
                _dictionary.Add(key,refNode);
                if (_dictionary.Count > _boundedCapacity)
                {
                    _ = _dictionary.Remove(_linkedList.First!.Value.Key);
                    _linkedList.RemoveFirst();
                }
            }
        }
    }
}