.net 2.0下 的HashSet——封装Dictionary

.net 3.5中的hashset用起来非常顺手，特别是元素数量不少（也不太多）又需要频繁进行搜索操作的时候。

最在 .net2.0 环境 + vs2008 下用了 LinqBridge （use linq in .net 2.0），觉得可以类似地可以写一个2.0的hashset，放在System.Collections.Generic命名空间里，在2.0的程序里引用，这样以后迁移到3.5+只要把引用去掉就可以了。 这个hashset通过封装Dictionary<TKey,TValue>实现。

using System;using System.Collections;using System.Diagnostics;using System.Runtime.Serialization;using System.Security;using System.Collections.Generic;namespace System.Collections.Generic{/// <summary>/// 在.net2.0环境下提供HashSet(Of T)类型的模拟实现/// </summary>/// <typeparam name="T">集合中的元素类型</typeparam>public class HashSet<T> : ICollection<T>, IEnumerable<T>, IEnumerable, ISerializable, IDeserializationCallback{private readonly Dictionary<T, object> dict;#region constructors/// <summary>/// Initializes a new instance of the System.Collections.Generic.HashSet<T> class/// that is empty and uses the default equality comparer for the set type./// </summary>public HashSet(){this.dict = new Dictionary<T, object>();}/// <summary>/// Initializes a new instance of the System.Collections.Generic.HashSet<T> class/// that uses the default equality comparer for the set type, contains elements/// copied from the specified collection, and has sufficient capacity to accommodate/// the number of elements copied./// </summary>/// <param name="collection">The collection whose elements are copied to the new set.</param>/// <exception cref="ArgumentNullException">collection is null.</exception>public HashSet(IEnumerable<T> collection){if (collection == null)throw new ArgumentNullException("collection");this.dict = new Dictionary<T, object>();foreach (T item in collection)this.dict[item] = null;}/// <summary>/// Initializes a new instance of the System.Collections.Generic.HashSet<T> class/// that is empty and uses the specified equality comparer for the set type./// </summary>/// <param name="comparer">/// The System.Collections.Generic.IEqualityComparer<T> implementation to use/// when comparing values in the set, or null to use the default System.Collections.Generic.EqualityComparer<T>/// implementation for the set type./// </param>public HashSet(IEqualityComparer<T> comparer){this.dict = new Dictionary<T, object>(comparer);}/// <summary>/// Initializes a new instance of the System.Collections.Generic.HashSet<T> class/// that uses the specified equality comparer for the set type, contains elements/// copied from the specified collection, and has sufficient capacity to accommodate/// the number of elements copied./// </summary>/// <param name="collection">The collection whose elements are copied to the new set.</param>/// <param name="comparer">/// The System.Collections.Generic.IEqualityComparer<T> implementation to use/// when comparing values in the set, or null to use the default System.Collections.Generic.EqualityComparer<T>/// implementation for the set type./// </param>/// <exception cref="ArgumentNullException">collection is null.</exception>public HashSet(IEnumerable<T> collection, IEqualityComparer<T> comparer){if (collection == null)throw new ArgumentNullException("collection");this.dict = new Dictionary<T, object>(comparer);foreach (T item in collection)this.dict[item] = null;}#endregion#region properties/// <summary>///  Gets the System.Collections.Generic.IEqualityComparer<T> object that is used///  to determine equality for the values in the set./// </summary>public IEqualityComparer<T> Comparer { get { return this.dict.Comparer; } }/// <summary>/// Gets the number of elements that are contained in a set./// </summary>public int Count { get { return this.dict.Count; } }#endregion#region methods/// <summary>/// Adds the specified element to a set./// </summary>/// <param name="item">The element to add to the set.</param>/// <returns>/// true if the element is added to the System.Collections.Generic.HashSet<T> object; /// false if the element is already present./// </returns>public bool Add(T item){if (this.dict.ContainsKey(item)){return false;}else{this.dict[item] = null;return true;}}/// <summary>/// Removes all elements from a System.Collections.Generic.HashSet<T> object./// </summary>public void Clear(){this.dict.Clear();}/// <summary>/// Determines whether a System.Collections.Generic.HashSet<T> object contains the specified element./// </summary>/// <param name="item">The element to locate in the System.Collections.Generic.HashSet<T> object.</param>/// <returns>true if the System.Collections.Generic.HashSet<T> object contains the specified element; otherwise, false.</returns>public bool Contains(T item){return this.dict.ContainsKey(item);}/// <summary>/// Copies the elements of a System.Collections.Generic.HashSet<T> object to an array./// </summary>/// <param name="array">/// The one-dimensional array that is the destination of the elements copied/// from the System.Collections.Generic.HashSet<T> object. The array must have/// zero-based indexing./// </param>/// <exception cref="System.ArgumentNullException">array is null.</exception>public void CopyTo(T[] array){if (array == null)throw new ArgumentNullException("array");this.dict.Keys.CopyTo(array, 0);}/// <summary>/// Copies the elements of a System.Collections.Generic.HashSet<T> object to an array, starting at the specified array index./// </summary>/// <param name="array">/// The one-dimensional array that is the destination of the elements copied/// from the System.Collections.Generic.HashSet<T> object. The array must have/// zero-based indexing./// </param>/// <param name="arrayIndex">The zero-based index in array at which copying begins.</param>/// <exception cref="System.ArgumentNullException">array is null.</exception>/// <exception cref="System.ArgumentOutOfRangeException">arrayIndex is less than 0.</exception>/// <exception cref="System.ArgumentException">arrayIndex is greater than the length of the destination array.  -or- count is larger than the size of the destination array.</exception>public void CopyTo(T[] array, int arrayIndex){if (array == null)throw new ArgumentNullException("array");if (arrayIndex < 0)throw new ArgumentOutOfRangeException();if (arrayIndex >= array.Length)throw new ArgumentException("arrayIndex is greater than the length of the destination array.");if (Count >= array.Length)throw new ArgumentException("the Count property is larger than the size of the destination array.");this.dict.Keys.CopyTo(array, arrayIndex);}/// <summary>/// Copies the specified number of elements of a System.Collections.Generic.HashSet<T> object to an array, /// starting at the specified array index./// </summary>/// <param name="array">The one-dimensional array that is the destination of the elements copied from the System.Collections.Generic.HashSet<T> object. The array must have zero-based indexing.</param>/// <param name="arrayIndex">The zero-based index in array at which copying begins.</param>/// <param name="count">The number of elements to copy to array.</param>/// <exception cref="System.ArgumentNullException">array is null.</exception>/// <exception cref="System.ArgumentOutOfRangeException">arrayIndex is less than 0.  -or- count is less than 0.</exception>/// <exception cref="System.ArgumentException">arrayIndex is greater than the length of the destination array.  -or- count is greater than the available space from the index to the end of the destination array.</exception>public void CopyTo(T[] array, int arrayIndex, int count){if (array == null)throw new ArgumentNullException("array");if (arrayIndex < 0 || count < 0)throw new ArgumentOutOfRangeException();if (arrayIndex >= array.Length)throw new ArgumentException("arrayIndex is greater than the length of the destination array.");if (count > array.Length - arrayIndex)throw new ArgumentException("count is greater than the available space from the index to the end of the destination array.");int copiedCount = 0;int currentIndex = arrayIndex;foreach (T item in this){array[currentIndex] = item;currentIndex++;copiedCount++;if (copiedCount >= count)break;}}/// <summary>/// Removes all elements in the specified collection from the current System.Collections.Generic.HashSet<T> object./// </summary>/// <param name="other">The collection of items to remove from the System.Collections.Generic.HashSet<T> object.</param>/// <exception cref="System.ArgumentNullException">other is null.</exception>public void ExceptWith(IEnumerable<T> other){if (other == null)throw new ArgumentNullException("other");foreach (T item in other)this.dict.Remove(item);}/// <summary>/// Modifies the current System.Collections.Generic.HashSet<T> object to contain/// only elements that are present in that object and in the specified collection./// </summary>/// <param name="other">The collection to compare to the current System.Collections.Generic.HashSet<T> object.</param>public void IntersectWith(IEnumerable<T> other){this.dict.Clear();foreach (T item in other)this.dict[item] = null;}/// <summary>/// Determines whether a System.Collections.Generic.HashSet<T> object is a proper subset of the specified collection./// </summary>/// <param name="other">The collection to compare to the current System.Collections.Generic.HashSet<T> object.</param>/// <returns>true if the System.Collections.Generic.HashSet<T> object is a proper subset of other; otherwise, false.</returns>/// <exception cref="System.ArgumentNullException">other is null.</exception>public bool IsProperSubsetOf(IEnumerable<T> other){return IsSubsetOf(other, true);}/// <summary>/// Determines whether a System.Collections.Generic.HashSet<T> object is a subset of the specified collection./// </summary>/// <param name="other">The collection to compare to the current System.Collections.Generic.HashSet<T> object.</param>/// <returns>true if the System.Collections.Generic.HashSet<T> object is a subset of other; otherwise, false.</returns>/// <exception cref="System.ArgumentNullException">other is null.</exception>public bool IsSubsetOf(IEnumerable<T> other){return IsSubsetOf(other, false);}private bool IsSubsetOf(IEnumerable<T> other, bool proper){if (other == null)throw new ArgumentNullException("other");int elementCount = 0;int mathingCount = 0;foreach (T item in other){elementCount++;if (this.dict.ContainsKey(item))mathingCount++;}if (proper)return mathingCount == this.dict.Count && elementCount > this.dict.Count;elsereturn mathingCount == this.dict.Count;}/// <summary>/// Determines whether a System.Collections.Generic.HashSet<T> object is a proper superset of the specified collection./// </summary>/// <param name="other">The collection to compare to the current System.Collections.Generic.HashSet<T> object.</param>/// <returns>true if the System.Collections.Generic.HashSet<T> object is a proper superset of other; otherwise, false.</returns>/// <exception cref="System.ArgumentNullException">other is null.</exception>public bool IsProperSupersetOf(IEnumerable<T> other){return IsSupersetOf(other, true);}/// <summary>/// Determines whether a System.Collections.Generic.HashSet<T> object is a superset of the specified collection./// </summary>/// <param name="other">The collection to compare to the current System.Collections.Generic.HashSet<T> object.</param>/// <returns>true if the System.Collections.Generic.HashSet<T> object is a superset of other; otherwise, false.</returns>/// <exception cref="System.ArgumentNullException">other is null.</exception>public bool IsSupersetOf(IEnumerable<T> other){return IsSupersetOf(other, false);}private bool IsSupersetOf(IEnumerable<T> other, bool proper){if (other == null)throw new ArgumentNullException("other");int elementCount = 0;foreach (T item in other){elementCount++;if (!this.dict.ContainsKey(item))return false;}if (proper)return elementCount < this.dict.Count;elsereturn true;}/// <summary>/// Determines whether the current System.Collections.Generic.HashSet<T> object overlaps the specified collection./// </summary>/// <param name="other">The collection to compare to the current System.Collections.Generic.HashSet<T> object.</param>/// <returns>true if the System.Collections.Generic.HashSet<T> object and other share at least one common element; otherwise, false.</returns>/// <exception cref="System.ArgumentNullException">other is null.</exception>public bool Overlaps(IEnumerable<T> other){if (other == null)throw new ArgumentNullException("other");foreach (T item in other){if (this.dict.ContainsKey(item))return true;}return false;}/// <summary>/// Removes the specified element from a System.Collections.Generic.HashSet<T> object./// </summary>/// <param name="item">The element to remove.</param>/// <returns>/// true if the element is successfully found and removed; otherwise, false./// This method returns false if item is not found in the System.Collections.Generic.HashSet<T> object./// </returns>public bool Remove(T item){if (this.dict.ContainsKey(item)){this.dict.Remove(item);return true;}else{return false;}}/// <summary>/// Removes all elements that match the conditions defined by the specified predicate from a System.Collections.Generic.HashSet<T> collection./// </summary>/// <param name="match">The System.Predicate<T> delegate that defines the conditions of the elements to remove.</param>/// <returns>The number of elements that were removed from the System.Collections.Generic.HashSet<T> collection.</returns>public int RemoveWhere(Predicate<T> match){int removeCount = 0;foreach (KeyValuePair<T, object> item in this.dict){if (match(item.Key)){this.dict.Remove(item.Key);removeCount++;}}return removeCount;}/// <summary>/// Determines whether a System.Collections.Generic.HashSet<T> object and the specified collection contain the same elements./// </summary>/// <param name="other">The collection to compare to the current System.Collections.Generic.HashSet<T> object.</param>/// <returns>true if the System.Collections.Generic.HashSet<T> object is equal to other; otherwise, false.</returns>/// <exception cref="System.ArgumentNullException">other is null.</exception>public bool SetEquals(IEnumerable<T> other){if (other == null)throw new ArgumentNullException("other");int containsCount = 0;foreach (T item in other){if (!this.dict.ContainsKey(item))return false;elsecontainsCount++;}return containsCount == this.dict.Count;}/// <summary>/// Modifies the current System.Collections.Generic.HashSet<T> object to contain only elements that are present either in that object or in the specified collection, but not both./// </summary>/// <param name="other">The collection to compare to the current System.Collections.Generic.HashSet<T>  object.</param>/// <exception cref="System.ArgumentNullException">other is null.</exception>public void SymmetricExceptWith(IEnumerable<T> other){if (other == null)throw new ArgumentNullException("other");HashSet<T> tmpSet = new HashSet<T>(other);foreach (T item in tmpSet){if (this.dict.ContainsKey(item))this.dict.Remove(item);elsethis.dict[item] = null;}}/// <summary>/// Sets the capacity of a System.Collections.Generic.HashSet<T> object to the/// actual number of elements it contains, rounded up to a nearby, implementation-specific/// value./// </summary>public void TrimExcess(){//do nothing}/// <summary>/// Modifies the current System.Collections.Generic.HashSet<T> object to contain/// all elements that are present in both itself and in the specified collection./// </summary>/// <param name="other">The collection to compare to the current System.Collections.Generic.HashSet<T> object.</param>/// <exception cref="System.ArgumentNullException">other is null.</exception>public void UnionWith(IEnumerable<T> other){if (other == null)throw new ArgumentNullException("other");foreach (T item in other)if (!this.dict.ContainsKey(item))this.dict[item] = null;}#endregion#region ICollection<T>, IEnumerable<T>, IEnumerable成员/// <summary>/// Returns an enumerator that iterates through a System.Collections.Generic.HashSet<T> object./// </summary>/// <returns>A System.Collections.Generic.HashSet<T>.Enumerator object for the System.Collections.Generic.HashSet<T> object.</returns>IEnumerator IEnumerable.GetEnumerator(){return this.dict.Keys.GetEnumerator();}void ICollection<T>.Add(T item){throw new NotImplementedException();}/// <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; }}/// <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> public IEnumerator<T> GetEnumerator(){return this.dict.Keys.GetEnumerator();}#endregion#region ISerializable 成员/// <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 IDeserializationCallback 成员/// <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){this.dict.OnDeserialization(sender);}#endregion#region Enumerator/// <summary>/// Enumerates the elements of a System.Collections.Generic.HashSet<T> object./// </summary>private struct Enumerator : IEnumerator<T>, IDisposable, IEnumerator{/// <summary>/// Gets the element at the current position of the enumerator./// </summary>/// <returns>The element in the System.Collections.Generic.HashSet<T> collection at the current position of the enumerator.</returns>public T Current{get { throw new NotImplementedException(); }}/// <summary>/// Releases all resources used by a System.Collections.Generic.HashSet<T>.Enumerator object./// </summary>public void Dispose(){throw new NotImplementedException();}/// <summary>/// Advances the enumerator to the next element of the System.Collections.Generic.HashSet<T> collection./// </summary>/// <returns>true if the enumerator was successfully advanced to the next element; false if the enumerator has passed the end of the collection.</returns>/// <exception cref="System.InvalidOperationException">The collection was modified after the enumerator was created.</exception>public bool MoveNext(){throw new NotImplementedException();}public void Reset(){throw new NotImplementedException();}object IEnumerator.Current{get { throw new NotImplementedException(); }}}#endregion}}