Question

How can I define two dimensional dynamic array?
If I want to use List<>, can I use it for two dimensions?

Answer 1

There’s no built-in dynamic equivalent of two-dimensional arrays that I’m aware of, but you can easily get at more or less the same functionaltiy.

Define a Coordinate class with this API:

public class Coordinate : IEquatable<Coordinate>
{
     public Coordinate(int x, int y);
     public int X { get; }
     public int Y { get; }
     // override Equals and GetHashcode...
}

You can now create a collection of these Coordinate instances.

If you create a HashSet<Coordinate> you will be guaranteed that you cannot add a Coordinate if it’s already added because it overrides Equals.

If you want, you can expand Coordinate to Coordinate<T> like this:

public class Coordinate<T> //...
{
    // previous stuff...

    public T Item { get; set; }
}

This will allow you to associate a strongly typed item with each coordinate, like this:

var items = new HashSet<Coordinate<string>>();
items.Add(new Coordinate<string>(1, 4) { Item = "Foo" });
items.Add(new Coordinate<string>(7, 19) { Item = "Foo" });
// ...