using System.Linq;

using FluentAssertions;

using static System.Linq.Enumerable;

public class Program

{

    public static void Main() {

        Matrix m1 = new(4,4); m1.SetMine(new(1,1));

        Matrix m2 = new(4,4); m2.SetMine(new(1,1));

        Matrix xx = new(4,4); xx.SetMine(new(2, 2));

​

        m2.Should().Be(m1); //same

        xx.Should().NotBe(m1); //different

    }

​

    public record struct Cell(char Value);

    public record Coordinate (int X, int Y);

    public class Matrix {

        private Cell[,] _matrix;

        public Matrix(int x, int y) {

            _matrix = new Cell[x, y];

            for (var m=0; m<x; m++)

                for (var n=0; n<y; n++)

                    _matrix[m, n] = new('.');

        }

        public void SetMine(Coordinate c)

            => _matrix[c.X, c.Y] = new('*');

        private string CellsAsString()

            => string.Concat(_matrix.OfType<Cell>().Select(c => c.Value));

        public override bool Equals(object other)

            => this.CellsAsString().Equals((other as Matrix)?.CellsAsString());

        public override int GetHashCode()

            => this.CellsAsString().GetHashCode();

    }

}