我真的很想在我的程序中使用哈希集。使用字典感觉很难看。我可能有一天会开始使用 .Net 3.5 的 VS2008，所以我的理想是即使我不能（或者我可以？）在 VS2005 中使用 hashsets，但当我开始使用 .NET 3.5 时，我不会不想为了切换到使用这些哈希集而进行很多更改（如果有的话）。
我想知道是否有人知道考虑到这一点设计的现有哈希集实现，或者在 VS2005 中使用 3.5 哈希集的方法。
【问题讨论】：
标签： c# .net visual-studio-2005
这是我为 2.0 编写的，它在内部使用 Dictionary
using System;
using System.Collections;
using System.Collections.Generic;
using System.Runtime.Serialization;
public class HashSet<T> : ICollection<T>, ISerializable, IDeserializationCallback
{
private readonly Dictionary<T, object> dict;
public HashSet()
{
dict = new Dictionary<T, object>();
}
public HashSet(IEnumerable<T> items) : this()
{
if (items == null)
{
return;
}
foreach (T item in items)
{
Add(item);
}
}
public HashSet<T> NullSet { get { return new HashSet<T>(); } }
#region ICollection<T> Members
public void Add(T item)
{
if (null == item)
{
throw new ArgumentNullException("item");
}
dict[item] = null;
}
/// <summary>
/// Removes all items from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only. </exception>
public void Clear()
{
dict.Clear();
}
public bool Contains(T item)
{
return dict.ContainsKey(item);
}
/// <summary>
/// Copies the items of the <see cref="T:System.Collections.Generic.ICollection`1"/> to an <see cref="T:System.Array"/>, starting at a particular <see cref="T:System.Array"/> index.
/// </summary>
/// <param name="array">The one-dimensional <see cref="T:System.Array"/> that is the destination of the items copied from <see cref="T:System.Collections.Generic.ICollection`1"/>. The <see cref="T:System.Array"/> must have zero-based indexing.</param><param name="arrayIndex">The zero-based index in <paramref name="array"/> at which copying begins.</param><exception cref="T:System.ArgumentNullException"><paramref name="array"/> is null.</exception><exception cref="T:System.ArgumentOutOfRangeException"><paramref name="arrayIndex"/> is less than 0.</exception><exception cref="T:System.ArgumentException"><paramref name="array"/> is multidimensional.-or-<paramref name="arrayIndex"/> is equal to or greater than the length of <paramref name="array"/>.-or-The number of items in the source <see cref="T:System.Collections.Generic.ICollection`1"/> is greater than the available space from <paramref name="arrayIndex"/> to the end of the destination <paramref name="array"/>.-or-Type T cannot be cast automatically to the type of the destination <paramref name="array"/>.</exception>
public void CopyTo(T[] array, int arrayIndex)
{
if (array == null) throw new ArgumentNullException("array");
if (arrayIndex < 0 || arrayIndex >= array.Length || arrayIndex >= Count)
{
throw new ArgumentOutOfRangeException("arrayIndex");
}
dict.Keys.CopyTo(array, arrayIndex);
}
/// <summary>
/// Removes the first occurrence of a specific object from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <returns>
/// true if <paramref name="item"/> was successfully removed from the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false. This method also returns false if <paramref name="item"/> is not found in the original <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </returns>
/// <param name="item">The object to remove from the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.</exception>
public bool Remove(T item)
{
return dict.Remove(item);
}
/// <summary>
/// Gets the number of items contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <returns>
/// The number of items contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </returns>
public int Count
{
get { return dict.Count; }
}
/// <summary>
/// Gets a value indicating whether the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
/// </summary>
/// <returns>
/// true if the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only; otherwise, false.
/// </returns>
public bool IsReadOnly
{
get
{
return false;
}
}
#endregion
public HashSet<T> Union(HashSet<T> set)
{
HashSet<T> unionSet = new HashSet<T>(this);
if (null == set)
{
return unionSet;
}
foreach (T item in set)
{
if (unionSet.Contains(item))
{
continue;
}
unionSet.Add(item);
}
return unionSet;
}
public HashSet<T> Subtract(HashSet<T> set)
{
HashSet<T> subtractSet = new HashSet<T>(this);
if (null == set)
{
return subtractSet;
}
foreach (T item in set)
{
if (!subtractSet.Contains(item))
{
continue;
}
subtractSet.dict.Remove(item);
}
return subtractSet;
}
public bool IsSubsetOf(HashSet<T> set)
{
HashSet<T> setToCompare = set ?? NullSet;
foreach (T item in this)
{
if (!setToCompare.Contains(item))
{
return false;
}
}
return true;
}
public HashSet<T> Intersection(HashSet<T> set)
{
HashSet<T> intersectionSet = NullSet;
if (null == set)
{
return intersectionSet;
}
foreach (T item in this)
{
if (!set.Contains(item))
{
continue;
}
intersectionSet.Add(item);
}
foreach (T item in set)
{
if (!Contains(item) || intersectionSet.Contains(item))
{
continue;
}
intersectionSet.Add(item);
}
return intersectionSet;
}
public bool IsProperSubsetOf(HashSet<T> set)
{
HashSet<T> setToCompare = set ?? NullSet;
// A is a proper subset of a if the b is a subset of a and a != b
return (IsSubsetOf(setToCompare) && !setToCompare.IsSubsetOf(this));
}
public bool IsSupersetOf(HashSet<T> set)
{
HashSet<T> setToCompare = set ?? NullSet;
foreach (T item in setToCompare)
{
if (!Contains(item))
{
return false;
}
}
return true;
}
public bool IsProperSupersetOf(HashSet<T> set)
{
HashSet<T> setToCompare = set ?? NullSet;
// B is a proper superset of a if b is a superset of a and a != b
return (IsSupersetOf(setToCompare) && !setToCompare.IsSupersetOf(this));
}
public List<T> ToList()
{
return new List<T>(this);
}
#region Implementation of ISerializable
/// <summary>
/// Populates a <see cref="T:System.Runtime.Serialization.SerializationInfo"/> with the data needed to serialize the target object.
/// </summary>
/// <param name="info">The <see cref="T:System.Runtime.Serialization.SerializationInfo"/> to populate with data. </param><param name="context">The destination (see <see cref="T:System.Runtime.Serialization.StreamingContext"/>) for this serialization. </param><exception cref="T:System.Security.SecurityException">The caller does not have the required permission. </exception>
public void GetObjectData(SerializationInfo info, StreamingContext context)
{
if (info == null) throw new ArgumentNullException("info");
dict.GetObjectData(info, context);
}
#endregion
#region Implementation of IDeserializationCallback
/// <summary>
/// Runs when the entire object graph has been deserialized.
/// </summary>
/// <param name="sender">The object that initiated the callback. The functionality for this parameter is not currently implemented. </param>
public void OnDeserialization(object sender)
{
dict.OnDeserialization(sender);
}
#endregion
#region Implementation of IEnumerable
/// <summary>
/// Returns an enumerator that iterates through the collection.
/// </summary>
/// <returns>
/// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
/// </returns>
/// <filterpriority>1</filterpriority>
public IEnumerator<T> GetEnumerator()
{
return dict.Keys.GetEnumerator();
}
/// <summary>
/// Returns an enumerator that iterates through a collection.
/// </summary>
/// <returns>
/// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
/// </returns>
/// <filterpriority>2</filterpriority>
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
#endregion
}
【讨论】：
Dictionary<> 关键方法（包括ConstainsKey）是经过哈希处理的 O(1) 实现，与具有类似目的的 HashSet 方法非常相似。 ContainsValue 是 O(n)。 Dictionary 的目的之一是提供对键的高速查找，而不是将索引用作数组。
您现在可以在 2.0 应用程序中使用 HashSet<T> - 只需引用 System.Core.dll 就可以了。
注意：这需要您安装.NET 3.5 framework，它是免费的，独立于 Visual Studio。安装完成后，您将拥有包含 HashSet<T> 类型的新 System.Core 程序集。由于 .NET 框架版本 2.0 - 3.5 都共享相同的 CLR，因此您可以在 2.0 应用程序中使用此程序集而不会出现任何问题。
【讨论】：
您可以使用Iesi.Collections（NHibernate 使用）或Mono's HashSet
【讨论】：
C5 Library 也有一个 HashSet 实现。
【讨论】：
我认为PowerCollections 库应该满足您的需求。它是一个开源库，包含 .NET 中缺少的几个集合类，包括 Set<T>、Bag<T>、MultiDictionary 等。它在 .NET 2.0 上运行。我已经使用它几年了，我对它非常满意。
【讨论】：
您可以使用 using 指令将 Dictionary 别名为 Hashset。不是一回事，但它可能会在以后为您简化事情。
【讨论】：