C＃ - 定义自定义按键的HashSet [英] C# - defining hashset with custom key

问题描述

我使用的是HashSet的词典在C＃来实现图形结构。我与HashSet的元素的唯一一个问题，当HashSet的关键是定制类。在这里，我有：

I am using the HashSet and Dictionary in C# to implement a Graph structure. I have a problem with the uniqueness of hashset elements when the hashset key is a customized class. Here I have:

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;
}

现在的问题是，当我有相同的顶点，我想将它们添加到图中，他们得到复制。我怎么可以定义HashSet中会明白我的顶点独特的方式？

The problem is that when I have same vertexes and I want to add them to the graph, they get duplicated. how can I define a way that the HashSet would understand the uniqueness of my vertexes?

推荐答案

选项：

• 覆盖等于和 GetHash code 在顶点（也许点为简单起见），很可能实施 [IEquatable] [1]; T＆GT; 作为你去
• 创建你自己的实施的IEqualityComparer＆LT;点＆GT; ，并传递到构造函数中的HashSet＆LT;点＆GT;

• Override Equals and GetHashCode in Vertex (and probably Point for simplicity), quite possibly implement [IEquatable][1]<T> as you go
• Create your own implementation of IEqualityComparer<Vertex> and pass that to the constructor of the HashSet<Vertex>

第一种选择可能是最简单的，但我的强烈的建议您点不可改变第一：可变类型（或类型包含可变类型）不好好哈希键。我可能会使其成为一个结构，也：

The first option is likely to be the simplest, but I would strongly recommend that you make Point immutable first: mutable types (or types containing mutable types) don't make good hash keys. I'd probably make it a struct, too:

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 GetHash code 和等于和实施 IEquatable＆LT ;＆GT; 在顶点过，如：

... then override GetHashCode and Equals and implement IEquatable<> in Vertex too, e.g.

// 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);
    }
}      

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