Question

If I want to use objects of this class as keys in a Dictionary, what do I need to do? (10.0, 20.0) shouldn’t exist as a key twice.

public class IntPoint
{
    public Int64 X { get; set; }
    public Int64 Y { get; set; }

    public IntPoint(Int64 X, Int64 Y)
    {
        this.X = X; this.Y = Y;
    }

    public override int GetHashCode()
    {
        return X.GetHashCode() ^ Y.GetHashCode();
    }
}

EDIT

public static Dictionary<IntPoint, List<int>> GetPolygonDuplicateIndixes(Polygon p)
{
    Dictionary<IntPoint, List<int>> d = new Dictionary<IntPoint, List<int>>();
    int i = 0;
    foreach(IntPoint point in p)
    {
        if(!d.ContainsKey(point))
        {
            d[point] = new List<int>();
        }
        d[point].Add(i);
        i++;
    }
    ...

I’m getting duplicates in d. Why? 22002, 1501 occurs twice in p.

Answer 1

If you look at the Dictionary documentation, you’ll see that if the keys implement
IEquatable, that equality implementation will be used instead.