feat: Add tictactoe AI mode

cmd/gg/main.go

@@ -31,6 +31,7 @@ func main() {
 			huh.NewOption("connect 4 (2 player)", "connect4"),
 			huh.NewOption("pong (2 player)", "pong"),
 			huh.NewOption("tictactoe (2 player)", "tictactoe"),
+			huh.NewOption("tictactoe (vs AI)", "tictactoe-ai"),
 		).
 		Value(&game).
 		Run()
@@ -46,6 +47,8 @@ func main() {
 		pong.Run()
 	case "tictactoe":
 		tictactoe.Run()
+	case "tictactoe-ai":
+		tictactoe.RunVsAi()
 	case "dodger":
 		dodger.Run()
 	case "hangman":

internal/app/tictactoe/engine/board.go

@@ -0,0 +1,91 @@
+package engine
+
+import "fmt"
+
+const (
+	P1    = 1
+	P2    = -1
+	EMPTY = 0
+)
+
+type Player = int
+
+type Board struct {
+	Size  int
+	Cells []int
+}
+
+func NewBoard(size int) *Board {
+	cells := make([]int, size*size)
+	for i := range cells {
+		cells[i] = EMPTY
+	}
+
+	return &Board{
+		Size:  size,
+		Cells: cells,
+	}
+}
+
+func (b *Board) GetCell(index int) (int, error) {
+	if index < 0 || index >= len(b.Cells) {
+		return 0, fmt.Errorf("invalid cell index: %d", index)
+	}
+
+	return b.Cells[index], nil
+}
+
+func (b *Board) SetCell(index int, player int) error {
+	if index < 0 || index >= len(b.Cells) {
+		return fmt.Errorf("invalid cell index: %d", index)
+	}
+
+	b.Cells[index] = player
+	return nil
+}
+
+func (b *Board) Load(cells []int) error {
+	if len(cells) != len(b.Cells) {
+		return fmt.Errorf("invalid cells length: %d", len(cells))
+	}
+
+	copy(b.Cells, cells)
+	return nil
+}
+
+func (b *Board) GetRowCol(index int) (int, int, error) {
+	if index < 0 || index >= len(b.Cells) {
+		return 0, 0, fmt.Errorf("invalid cell index: %d", index)
+	}
+
+	return index / b.Size, index % b.Size, nil
+}
+
+func (b *Board) ChangePerspective() {
+	for i := range b.Cells {
+		b.Cells[i] *= -1
+	}
+}
+
+func (b *Board) Copy() *Board {
+	newBoard := NewBoard(b.Size)
+	copy(newBoard.Cells, b.Cells)
+	return newBoard
+}
+
+func (b *Board) Print() {
+	for i := 0; i < b.Size; i++ {
+		for j := 0; j < b.Size; j++ {
+			cell, _ := b.GetCell(i*b.Size + j)
+			if cell == P1 {
+				fmt.Print("O")
+			} else if cell == P2 {
+				fmt.Print("X")
+			} else {
+				fmt.Print(".")
+			}
+		}
+		fmt.Println()
+	}
+	fmt.Println()
+}

internal/app/tictactoe/engine/engine.go

@@ -0,0 +1,145 @@
+package engine
+
+type Engine struct {
+	ai AI
+}
+
+func NewEngine(depth int) *Engine {
+	engine := &Engine{}
+	mcts := NewMCTS(engine, depth)
+	engine.ai = mcts
+
+	return engine
+}
+
+func (e *Engine) GetLegalMoves(board *Board) []int {
+	var moves []int
+	for i, cell := range board.Cells {
+		if cell == EMPTY {
+			moves = append(moves, i)
+		}
+	}
+	return moves
+}
+
+func (e *Engine) PlayMove(board *Board, player int, move int) error {
+	return board.SetCell(move, player)
+}
+
+func (e *Engine) GetOpponent(player int) int {
+	return -player
+}
+
+func (e *Engine) CheckGameOver(board *Board, lastMove int) (bool, int) {
+	if lastMove == -1 {
+		return false, 0
+	}
+
+	if e.CheckWin(board, lastMove) {
+		absValue := P1 * P2 * -1
+		return true, absValue
+	}
+
+	if len(e.GetLegalMoves(board)) == 0 {
+		return true, 0
+	}
+
+	return false, 0
+}
+
+func (e *Engine) CheckWin(board *Board, lastMove int) bool {
+	player, err := board.GetCell(lastMove)
+	if err != nil {
+		panic(err)
+	}
+	if player == EMPTY {
+		return false
+	}
+
+	row, col, err := board.GetRowCol(lastMove)
+	if err != nil {
+		panic(err)
+	}
+
+	if e.checkRow(board, row, player) {
+		return true
+	}
+
+	if e.checkCol(board, col, player) {
+		return true
+	}
+
+	if e.checkDiagonal(board, player) {
+		return true
+	}
+
+	return false
+}
+
+func (e *Engine) checkRow(board *Board, row, player int) bool {
+	for i := 0; i < board.Size; i++ {
+		cell, err := board.GetCell(row*board.Size + i)
+		if err != nil {
+			panic(err)
+		}
+
+		if cell != player {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (e *Engine) checkCol(board *Board, col, player int) bool {
+	for i := 0; i < board.Size; i++ {
+		cell, err := board.GetCell(i*board.Size + col)
+		if err != nil {
+			panic(err)
+		}
+
+		if cell != player {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (e *Engine) checkDiagonal(board *Board, player int) bool {
+	sum := 0
+	// Left to right
+	for i := 0; i < board.Size; i++ {
+		cell, err := board.GetCell(i*board.Size + i)
+		if err != nil {
+			panic(err)
+		}
+
+		if cell == player {
+			sum += player
+		}
+	}
+
+	if sum == board.Size*player {
+		return true
+	}
+
+	sum = 0
+	// Right to left
+	for i := 0; i < board.Size; i++ {
+		cell, err := board.GetCell(i*board.Size + board.Size - i - 1)
+		if err != nil {
+			panic(err)
+		}
+
+		if cell == player {
+			sum += player
+		}
+	}
+
+	if sum == board.Size*player {
+		return true
+	}
+
+	return false
+}