C# – 使用自定义键定义哈希集

我使用C#中的HashSet和Dictionary来实现一个Graph结构.当哈希集密钥是自定义类时,我有一个哈希集元素的唯一性问题.在这里我有

public class Point
{
    public int x { get; set; }
    public int y { get; set; }
}

public class Vertex
{
    public Vertex(Point point)
    {
        VertexLabel = point;
    }

    public Point VertexLabel { get; private set; }
}

 public class Edge
{
    public Edge(Vertex to,Vertex from,double weight)
    {
        FromVertex = from;
        ToVertex = to;
        Weight = weight;
    }

    public Vertex FromVertex { get; private set; }
    public Vertex ToVertex { get; private set; }
    public double Weight { get; private set; }
}

public class Graph
{
    public Graph()
    {
        _Vertexes = new HashSet<Vertex>();
        _VertexEdgeMapping = new Dictionary<Vertex,LinkedList<Edge>>();
    }
    private HashSet<Vertex> _Vertexes;
    private Dictionary<Vertex,LinkedList<Edge>> _VertexEdgeMapping;
}

问题是,当我有相同的顶点,我想将它们添加到图形,它们被重复.我如何定义一个方法,HashSet将会理解我的顶点的唯一性？

解决方法

选项：

>在顶点中覆盖Equals和GetHashCode(并且为了简单起见可能是Point),很可能实现[IEquatable] [1]< T>当你去时
>创建自己的实现IEqualityComparer< Vertex>并将其传递给HashSet< Vertex>的构造函数

第一个选项可能是最简单的,但我强烈建议您使Point不可变的第一个：可变类型(或包含可变类型的类型)不会产生好的散列键.我也可能会使它成为一个结构体：

public struct Point : IEquatable<Point>
{
    private readonly int x,y;

    public int X { get { return x; } }
    public int Y { get { return y; } }

    public Point(int x,int y)
    {
        this.x = x;
        this.y = y;
    }

    public override int GetHashCode()
    {
        return 31 * x + 17 * y; // Or something like that
    }

    public override bool Equals(object obj)
    {
        return obj is Point && Equals((Point) obj);
    }

    public bool Equals(Point p)
    {
        return x == p.x && y == p.y;
    }

    // Todo: Consider overloading the == and != operators
}

…然后覆盖GetHashCode和Equals并实现IEquatable<>在顶点也可以.

// Note: sealed to avoid oddities around equality and inheritance
public sealed class Vertex : IEquatable<Vertex>
{
    public Vertex(Point point)
    {
        VertexLabel = point;
    }

    public Point VertexLabel { get; private set; }

    public override int GetHashCode()
    {
        return VertexLabel.GetHashCode();
    }

    public override bool Equals(object obj)
    { 
        return Equals(obj as Vertex);
    }

    public bool Equals(Vertex vertex)
    {
        return vertex != null && vertex.VertexLabel.Equals(VertexLabel);
    }
}