HashSet
HashSet类的特征：
- HashSet < T >类提供高性能的设置操作。集合是不包含重复元素且其元素没有特定顺序的集合。
- HashSet < T >对象的容量是该对象可以容纳的元素数。
- 当元素添加到对象时，HashSet < T >对象的容量会自动增加。
- HashSet < T >集合未排序，并且不能包含重复的元素。
- HashSet < T >提供许多数学集合运算，例如集合加法(联合)和集合减法。
建设者
| Constructor | Description |
|---|---|
| HashSet() | Initializes a new instance of the HashSet class that is empty and uses the default equality comparer for the set type. |
| HashSet(IEnumerable) | Initializes a new instance of the HashSet 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. |
| HashSet(IEnumerable, IEqualityComparer) | Initializes a new instance of the HashSet 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. |
| HashSet(IEqualityComparer) | Initializes a new instance of the HashSet class that is empty and uses the specified equality comparer for the set type. |
| HashSet(Int32) | Initializes a new instance of the HashSet class that is empty, but has reserved space for capacity items and uses the default equality comparer for the set type. |
| HashSet(Int32, IEqualityComparer) | Initializes a new instance of the HashSet class that uses the specified equality comparer for the set type, and has sufficient capacity to accommodate capacity elements. |
| HashSet(SerializationInfo, StreamingContext) | Initializes a new instance of the HashSet class with serialized data. |
例子：
// C# code to create a HashSet
using System;
using System.Collections.Generic;
class GFG {
// Driver code
public static void Main()
{
// Creating a HashSet of odd numbers
HashSet odd = new HashSet();
// Inserting elements in HashSet
for (int i = 0; i < 5; i++) {
odd.Add(2 * i + 1);
}
// Displaying the elements in the HashSet
foreach(int i in odd)
{
Console.WriteLine(i);
}
}
}
输出：
1
3
5
7
9
特性
| Property | Description |
|---|---|
| Comparer | Gets the IEqualityComparer object that is used to determine equality for the values in the set. |
| Count | Gets the number of elements that are contained in a set. |
例子：
// C# code to get the number of
// elements that are contained in HashSet
using System;
using System.Collections.Generic;
class GFG {
// Driver code
public static void Main()
{
// Creating a HashSet of integers
HashSet mySet = new HashSet();
// Inserting elements in HashSet
for (int i = 0; i < 5; i++) {
mySet.Add(i * 2);
}
// To get the number of
// elements that are contained in HashSet
Console.WriteLine(mySet.Count);
}
}
输出：
5
方法
| Method | Description |
|---|---|
| Add(T) | Adds the specified element to a set. |
| Clear() | Removes all elements from a HashSet object. |
| Contains(T) | Determines whether a HashSet object contains the specified element. |
| CopyTo() | Copies the elements of a HashSet collection to an array. |
| CreateSetComparer() | Returns an IEqualityComparer object that can be used for equality testing of a HashSet object. |
| Equals(Object) | Determines whether the specified object is equal to the current object. |
| ExceptWith(IEnumerable) | Removes all elements in the specified collection from the current HashSet object. |
| GetEnumerator() | Returns an enumerator that iterates through a HashSet object. |
| GetHashCode() | Serves as the default hash function. |
| GetObjectData(SerializationInfo, StreamingContext) | Implements the ISerializable interface and returns the data needed to serialize a HashSet object. |
| GetType() | Gets the Type of the current instance. |
| IntersectWith(IEnumerable) | Modifies the current HashSet object to contain only elements that are present in that object and in the specified collection. |
| IsProperSubsetOf(IEnumerable) | Determines whether a HashSet object is a proper subset of the specified collection. |
| IsProperSupersetOf(IEnumerable) | Determines whether a HashSet object is a proper superset of the specified collection. |
| IsSubsetOf(IEnumerable) | Determines whether a HashSet object is a subset of the specified collection. |
| IsSupersetOf(IEnumerable) | Determines whether a HashSet object is a superset of the specified collection. |
| MemberwiseClone() | Creates a shallow copy of the current Object. |
| OnDeserialization(Object) | Implements the ISerializable interface and raises the deserialization event when the deserialization is complete. |
| Overlaps(IEnumerable) | Determines whether the current HashSet object and a specified collection share common elements. |
| Remove(T) | Removes the specified element from a HashSet object. |
| RemoveWhere(Predicate) | Removes all elements that match the conditions defined by the specified predicate from a HashSet collection. |
| SetEquals(IEnumerable) | Determines whether a HashSet object and the specified collection contain the same elements. |
| SymmetricExceptWith(IEnumerable) | Modifies the current HashSet object to contain only elements that are present either in that object or in the specified collection, but not both. |
| ToString() | Returns a string that represents the current object. |
| TrimExcess() | Sets the capacity of a HashSet object to the actual number of elements it contains, rounded up to a nearby, implementation-specific value. |
| TryGetValue(T, T) | Searches the set for a given value and returns the equal value it finds, if any. |
| UnionWith(IEnumerable) | Modifies the current HashSet object to contain all elements that are present in itself, the specified collection, or both. |
例子：
// C# code to Check if a HashSet is
// a subset of the specified collection
using System;
using System.Collections.Generic;
class GFG {
// Driver code
public static void Main()
{
// Creating a HashSet of integers
HashSet mySet1 = new HashSet();
// Inserting elements in HashSet
// mySet1 only contains even numbers less than
// equal to 10
for (int i = 1; i <= 5; i++)
mySet1.Add(2 * i);
// Creating a HashSet of integers
HashSet mySet2 = new HashSet();
// Inserting elements in HashSet
// mySet2 contains all numbers from 1 to 10
for (int i = 1; i <= 10; i++)
mySet2.Add(i);
// Check if a HashSet mySet1 is a subset
// of the HashSet mySet2
Console.WriteLine(mySet1.IsSubsetOf(mySet2));
}
}
输出：
True
例子：
// C# code to check if a HashSet
// contains the specified element
using System;
using System.Collections.Generic;
class GFG {
// Driver code
public static void Main()
{
// Creating a HashSet of strings
HashSet mySet = new HashSet();
// Inserting elements in HashSet
mySet.Add("DS");
mySet.Add("C++");
mySet.Add("Java");
mySet.Add("JavaScript");
// Check if a HashSet contains
// the specified element
if (mySet.Contains("Java"))
Console.WriteLine("Required Element is present");
else
Console.WriteLine("Required Element is not present");
}
}
输出：
Required Element is present
参考：
- https://docs.microsoft.com/zh-cn/dotnet/api/system.collections.generic.hashset-1?view=netframework-4.7.2