我是使用Generics并尝试使用C#中的Generic Circular双向链表实现LRU缓存的新手。我有几个问题。请帮帮我
1)在我的LRUCache构造函数中正在执行此操作
head = new Node<T>(default(T), default(T));
这是不对的,我想用一些默认键值对(-1,-1)数据而不是类型默认值初始化我的头。
2)在我的get中,我检查节点是基于键并返回默认值(T)为空。但我想返回null本身。
这是我的代码
public class Node<T>
{
public KeyValuePair<T, T> KeyValue { get; set; }
public Node<T> Next { get; set; }
public Node<T> Previous { get; set; }
public Node(T key, T value)
{
this.KeyValue = new KeyValuePair<T, T>(key, value);
Next = null;
Previous = null;
}
}
public class LRUCache<T>
{
private readonly int capacity;
private int count;
private readonly Node<T> head;
private readonly Dictionary<T, Node<T>> myDictionary;
public LRUCache(int capacity)
{
head = new Node<T>(default(T), default(T));
head.Next = head;
head.Previous = head;
this.capacity = capacity;
myDictionary = new Dictionary<T, Node<T>>();
}
public void set(T key, T value)
{
Node<T> node;
myDictionary.TryGetValue(key, out node);
if (node == null)
{
if (this.count == this.capacity)
{
// remove the last element
myDictionary.Remove(head.Previous.KeyValue.Key);
head.Previous = head.Previous.Previous;
head.Previous.Next = head;
count--;
}
// create new node and add to dictionary
var newNode = new Node<T>(key, value);
myDictionary[key] = newNode;
this.InsertAfterTheHead(newNode);
// increase count
count++;
}
else
{
node.KeyValue = new KeyValuePair<T, T>(key, value);
this.MoveToFirstElementAfterHead(node);
}
}
public T get(T key)
{
Node<T> node;
myDictionary.TryGetValue(key, out node);
if (node == null)
{
return default(T);
}
this.MoveItToFirstElementAfterHead(node);
return node.KeyValue.Value;
}
}
答案 0 :(得分:0)
假设节点中包含的值是包含用作键的属性的类,请尝试以下操作:
public abstract class Node<TNode, TNodeSupport, TKey, TValue>
where TNode : Node<TNode, TNodeSupport, TKey, TValue>
where TNodeSupport : Node<TNode, TNodeSupport, TKey, TValue>.BaseNodeSupport, new()
where TValue : class
{
protected static readonly TNodeSupport Support = new TNodeSupport();
public KeyValuePair<TKey, TValue> KeyValue { get; set; }
public TNode Next { get; set; }
public TNode Previous { get; set; }
protected Node(TValue value)
{
this.KeyValue = new KeyValuePair<TKey, TValue>(Support.GetKeyFromValue(value), value);
Next = null;
Previous = null;
}
public class LRUCache
{
private readonly int capacity;
private int count;
private readonly TNode head;
private readonly Dictionary<TKey, TNode> myDictionary;
public LRUCache(int capacity)
{
head = Support.CreateHeadNode();
head.Next = head;
head.Previous = head;
this.capacity = capacity;
myDictionary = new Dictionary<TKey, TNode>();
}
public void set(TValue value)
{
TKey key = Support.GetKeyFromValue(value);
TNode node;
myDictionary.TryGetValue(key, out node);
if (node == null)
{
if (this.count == this.capacity)
{
// remove the last element
myDictionary.Remove(head.Previous.KeyValue.Key);
head.Previous = head.Previous.Previous;
head.Previous.Next = head;
count--;
}
// create new node and add to dictionary
var newNode = Support.CreateNodeFromValue(value);
myDictionary[key] = newNode;
this.InsertAfterTheHead(newNode);
// increase count
count++;
}
else
{
node.KeyValue = new KeyValuePair<TKey, TValue>(key, value);
this.MoveToFirstElementAfterHead(node);
}
}
public TValue get(TKey key)
{
TNode node;
myDictionary.TryGetValue(key, out node);
if (node == null)
{
return null;
}
this.MoveItToFirstElementAfterHead(node);
return node.KeyValue.Value;
}
}
public abstract class BaseNodeSupport
{
public abstract TKey GetKeyFromValue(TValue value);
public abstract TNode CreateNodeFromValue(TValue value);
public abstract TNode CreateHeadNode();
}
}
定义您的节点和项目:
public class Item
{
public Guid Id;
public String Data;
}
public class ItemNode : Node<ItemNode, ItemNode.Support, Guid, Item>
{
public class NodeSupport : BaseNodeSupport
{
public override Guid GetKeyFromValue(Item value) { return value.Id; }
public override ItemNode CreateNodeFromValue(Item value) {return new ItemNode(value)
public override ItemNode CreateHeadNode() { return new ItemNode(new Item(){Id = Guid.Empty, Data = String.Empty}); }
}
public ItemNode(Item item) : base(item) {}
}
像这样使用:
public class Program
{
static void Main()
{
var cache = new ItemNode.LRUCache(100);
}
}
在此解决方案中,Node是一个类和一个通用/参数命名空间,用于保存来自第三方库或本地定义的项目。
TNodeSupport类用作单例,提供在整个Node命名空间中使用的三个支持函数。第一个函数接受一个项目并从该项目返回密钥。第二个函数从项目创建TNode。第三个函数使用默认的空项创建默认头节点。
LRUCache包含在Node通用命名空间中,因此它可以访问它所需的泛型类型参数以便运行。 LRUCache逻辑实现与作者的原始实现大致相同。
在定义子类Node的示例中,ItemNode是参数化的子类/子名称空间。 ItemNode为TNode参数指定自身,为TNodeSupport参数指定ItemNode.NodeSupport,为TKey参数指定Guid,为TValue参数指定Item。
Item类是一个人为的类,用于包含一些数据以及将用作项目键的Id。
Item.NodeSupport类派生自Node.BaseNodeSupport类,并覆盖三个支持函数。在GetKeyFromValue方法中,它返回所提供的Item实例的Id属性。在CreateNodeFromValue方法中,它返回使用提供的Item实例构造的ItemNode。在CreateHeadNode方法中,它返回一个新的ItemNode,该ItemNode由一个新的Item构成,该Item包含Id的Guid.Empty和数据的String.Empty。
在Program类中,我们实例化ItemNode.LRUCache以包含包含Items的ItemNode实例。