using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var testDict = new Dictionary<UnorderedPair<int>, string>();

        testDict.Add(new UnorderedPair<int>(1, 2), "Hello World!");

        Console.WriteLine(testDict[new UnorderedPair<int>(2, 1)]);

    }

}

​

#nullable enable

public class UnorderedPair<T> : IEquatable<UnorderedPair<T>>

{

    private static IEqualityComparer<T> comparer = EqualityComparer<T>.Default;

    public T X { get; }

    public T Y { get; }

    public UnorderedPair(T x, T y)

    {

        X = x;

        Y = y;

    }

​

    public bool Equals(UnorderedPair<T>? other)

    {

        if(other is null)

        {

            return false;

        }

​

        if (ReferenceEquals(this, other))

        {

            return true;

        }

        // For equality simply include the swapped check

        return

                comparer.Equals(X, other.X) && comparer.Equals(Y, other.Y)

            ||

                comparer.Equals(X, other.Y) && comparer.Equals(Y, other.X);

    }

​

    public override bool Equals(object? obj)

    {

        return Equals(obj as UnorderedPair<T>);

    }

​

    public override int GetHashCode()

    {

        unchecked

        {

            return

                    (X is null ? 0 : comparer.GetHashCode(X))

                +

                    (Y is null ? 0 : comparer.GetHashCode(Y));

        }

    }

​

    public static bool operator ==(UnorderedPair<T>? left, UnorderedPair<T>? right)

    {

        return Equals(left, right);

    }

​

    public static bool operator !=(UnorderedPair<T>? left, UnorderedPair<T>? right)

    {

        return !Equals(left, right);

    }

}

#nullable disable