Sparse Matrix

sparsematrix.cs

public struct Position : IEquatable<Position>
{
    private readonly int _x;
    private readonly int _y;

    public int X { get { return _x; } }
    public int Y { get { return _y; } }

    public Position(int x, int y)
    {
        _x = x;
        _y = y;
    }

    public override int GetHashCode()
    {
        unchecked
        {
            int hash = 17;
            hash = hash * 23 + X.GetHashCode();
            hash = hash * 23 + Y.GetHashCode();
            return hash;
        }
    }

    public override bool Equals(object obj)
    {
        if (obj is Position)
            return Equals((Position)obj);
        return false;
    }

    public bool Equals(Position other)
    {
        return X == other.X && Y == other.Y;
    }

    public static bool operator ==(Position lhs, Position rhs)
    {
        return lhs.X == rhs.X && lhs.Y == rhs.Y;
    }

    public static bool operator !=(Position lhs, Position rhs)
    {
        return lhs.X != rhs.X || lhs.Y != rhs.Y;
    }
}

public class SparseMatrix<TCell> 
    : IEnumerable<KeyValuePair<Position, TCell>>
{
    private readonly IDictionary<Position, TCell> _cells;

    public SparseMatrix()
    {
        _cells = new Dictionary<Position, TCell>();
    }

    public int Count { get { return _cells.Count; } }

    public TCell this[int x, int y]
    {
        get
        {
            TCell ret;
            if (_cells.TryGetValue(new Position(x, y), out ret))
                return ret;
            return default(TCell);
        }
        set
        {
            if (_cells.ContainsKey(new Position(x, y)))
            {
                if (Equals(value, default(TCell)))
                    _cells.Remove(new Position(x, y));
                else
                    _cells[new Position(x, y)] = value;
            }
            else
            {
                if (Equals(value, default(TCell)))
                    return;

                _cells.Add(new Position(x, y), value);
            }
        }
    }

    public IEnumerator<KeyValuePair<Position, TCell>> GetEnumerator()
    {
        return _cells.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}