public static void Print(this Playground playground)
{
ConsoleColor foreground = Console.ForegroundColor;
for (var r = 0; r < 3; r++)
{
Console.WriteLine("+---+---+---+");
for (var c = 0; c < 3; c++)
{
Field field = playground.Fields[r * 3 + c];
Console.Write("| ");
Console.ForegroundColor = field.IsEmpty ? ConsoleColor.Gray : ConsoleColor.Green;
Console.Write(GetFieldValue(field));
Console.ForegroundColor = foreground;
Console.Write(" ");
}
Console.WriteLine("|");
}
Console.WriteLine("+---+---+---+");
}
public static IEnumerable <Field> EmptyFields(this Playground playground)
{
if (playground == null)
{
throw new ArgumentNullException(nameof(playground));
}
return(playground.Fields.Where(f => f.IsEmpty));
}
/// <summary>
/// Calculates the best move for given playground state.
/// </summary>
/// <param name="playground">Game playground.</param>
/// <returns>
/// Returns index of field of the best move for player.
/// </returns>
public (bool CanTurn, int Index) CalulateBestMove(Playground playground)
{
if (playground == null)
{
throw new ArgumentNullException(nameof(playground));
}
FieldScore result = MiniMax(playground, true);
return(result.Index > 0
? (true, result.Index)
: (false, 0));
}
/// <summary>
/// Evaluate every possible move using minimax algorithm.
/// </summary>
/// <param name="playground">Game playground.</param>
/// <param name="isMaximizing"><c>true</c> if player's move, <c>false</c> if opponent's move.</param>
/// <returns>
/// Returns field-score.
/// </returns>
private FieldScore MiniMax(Playground playground, bool isMaximizing)
{
PlaygroundState state = playground.GetState();
// board is in final state, return score immediately
// (since we are not aware of previous move (chosen field)
// we return only score part)
if (state.State != GameState.NotComplete)
{
return(state.State == GameState.Tie
? new FieldScore {
Score = 0
}
: _player.Equals(state.Player)
? new FieldScore {
Score = 1
}
: new FieldScore {
Score = -1
});
}
Player currentPlayer = isMaximizing
? _player
: _opponent;
// calculate scores for each possible move
// (NB! recursion is about to happen)
IEnumerable <FieldScore> moves = playground.EmptyFields()
.Select(
f => new FieldScore
{
Index = f.Index,
Score = MiniMax(playground.Turn(f.Index, currentPlayer), !isMaximizing).Score
});
// captain obvious to the service:
// player - get the highest score (ORDER BY score DESC)
// opponent - get the lowest score (ORDER BY score ASC)
moves = isMaximizing
? moves.OrderByDescending(m => m.Score)
: moves.OrderBy(m => m.Score);
return(moves.First());
}
static void Main(string[] args)
{
var p1 = new Player('X');
var p2 = new Player('O');
var s1 = new Solver(p1, p2);
var s2 = new Solver(p2, p1);
var playground = new Playground();
playground = playground.Turn(s1.CalulateBestMove(playground).Index, p1);
playground.Print();
playground = playground.Turn(s2.CalulateBestMove(playground).Index, p2);
playground.Print();
playground = playground.Turn(s1.CalulateBestMove(playground).Index, p1);
playground.Print();
playground = playground.Turn(s2.CalulateBestMove(playground).Index, p2);
playground.Print();
playground = playground.Turn(s1.CalulateBestMove(playground).Index, p1);
playground.Print();
playground = playground.Turn(s2.CalulateBestMove(playground).Index, p2);
playground.Print();
playground = playground.Turn(s1.CalulateBestMove(playground).Index, p1);
playground.Print();
playground = playground.Turn(s2.CalulateBestMove(playground).Index, p2);
playground.Print();
playground = playground.Turn(s2.CalulateBestMove(playground).Index, p1);
playground.Print();
Debugger.Break();
}
