Update and add chess piece style, prevent repeated falling, victory &…

docs/tictactoe.rst

@@ -1,6 +1,44 @@
 Tic Tac Toe
 ===========
 
-A paper-and-pencil game for two players.
+A single-player vs computer Tic Tac Toe game with the following features:
+
+- **Colored and styled pieces**:
+  X in blue, O in red, with thicker lines for clarity.
+- **Move validation**:
+  Prevents placing a piece on an occupied square.
+- **Win and draw detection**:
+  Automatically detects and displays a result message when someone
+  wins or when the board is full (draw).
+- **Smart AI opponent**:
+  Uses the Minimax algorithm for optimal play, ensuring a
+  challenging game.
+
+Gameplay
+--------
+
+1. **Starting the game**:
+
+   .. code-block:: python
+
+      python tictactoe.py
+
+2. **Player moves**:
+   The human player uses X (blue) and always moves first. Click on
+   any empty square in the 3×3 grid to place your X.
+
+3. **Computer response**:
+   After your move, the computer (O in red) will calculate its optimal
+   move and place an O after a brief delay.
+
+4. **Winning**:
+   The first player to align three of their own pieces in a row
+   (horizontal, vertical, or diagonal) wins.
+
+5. **Draw**:
+   If all nine squares are filled without a winner, the game ends
+   in a draw.
 
 .. literalinclude:: ../src/freegames/tictactoe.py
+   :language: python
+   :linenos:

src/freegames/tictactoe.py

@@ -1,64 +1,157 @@
-"""Tic Tac Toe
-
-Exercises
-
-1. Give the X and O a different color and width.
-2. What happens when someone taps a taken spot?
-3. How would you detect when someone has won?
-4. How could you create a computer player?
-"""
-
 from turtle import *
 
 from freegames import line
 
+# ——— 全局状态 ———
+state = {
+    'player': 0,                   # 0 = X（人），1 = O（电脑）
+    'board': [[None]*3 for _ in range(3)],
+    'game_over': False,
+}
 
+# 绘制格子
 def grid():
     """Draw tic-tac-toe grid."""
     line(-67, 200, -67, -200)
-    line(67, 200, 67, -200)
+    line( 67, 200,  67, -200)
     line(-200, -67, 200, -67)
-    line(-200, 67, 200, 67)
-
+    line(-200,  67, 200,  67)
 
+# 画 X
 def drawx(x, y):
-    """Draw X player."""
+    """Draw X player in blue, width=4."""
+    color('blue')
+    width(4)
     line(x, y, x + 133, y + 133)
     line(x, y + 133, x + 133, y)
 
-
+# 画 O
 def drawo(x, y):
-    """Draw O player."""
+    """Draw O player in red, width=4."""
     up()
     goto(x + 67, y + 5)
     down()
+    color('red')
+    width(4)
     circle(62)
 
-
+# 将点击坐标归整到格子左下角
 def floor(value):
-    """Round value down to grid with square size 133."""
     return ((value + 200) // 133) * 133 - 200
 
+# 检测胜利
+def check_win():
+    b = state['board']
+    # 行、列检测
+    for i in range(3):
+        if b[i][0] is not None and b[i][0] == b[i][1] == b[i][2]:
+            return b[i][0]
+        if b[0][i] is not None and b[0][i] == b[1][i] == b[2][i]:
+            return b[0][i]
+    # 对角线
+    if b[0][0] is not None and b[0][0] == b[1][1] == b[2][2]:
+        return b[0][0]
+    if b[0][2] is not None and b[0][2] == b[1][1] == b[2][0]:
+        return b[0][2]
+    # 平局
+    if all(all(cell is not None for cell in row) for row in b):
+        return -1
+    return None
+
+def evaluate():
+    """胜利时得分：电脑 O 赢 +1，人 X 赢 -1，平局或未结束 0"""
+    winner = check_win()
+    if winner == 1:   # O (电脑)
+        return +1
+    if winner == 0:   # X (人)
+        return -1
+    return 0          # 平局 or 未结束
+
+def minimax(is_maximizing):
+    """Minimax 递归，返回 (最佳分值, (row, col) 最佳落子)"""
+    score = evaluate()
+    if score != 0 or all(all(cell is not None for cell in row) for row in state['board']):
+        # 终止：有人赢或满盘
+        return score, None
+
+    if is_maximizing:
+        best = (-2, None)  # 初始化为比最小值还低
+        for r in range(3):
+            for c in range(3):
+                if state['board'][r][c] is None:
+                    state['board'][r][c] = 1  # 电脑落 O
+                    val, _ = minimax(False)
+                    state['board'][r][c] = None
+                    if val > best[0]:
+                        best = (val, (r, c))
+        return best
+    else:
+        worst = (2, None)   # 初始化为比最大值还高
+        for r in range(3):
+            for c in range(3):
+                if state['board'][r][c] is None:
+                    state['board'][r][c] = 0  # 玩家落 X
+                    val, _ = minimax(True)
+                    state['board'][r][c] = None
+                    if val < worst[0]:
+                        worst = (val, (r, c))
+        return worst
+
+# 落子回调
+def tap(x, y):
+    if state['game_over']:
+        return
 
-state = {'player': 0}
-players = [drawx, drawo]
+    # 计算格子索引
+    fx = floor(x)
+    fy = floor(y)
+    col = int((fx + 200) // 133)
+    row = int((fy + 200) // 133)
 
+    # 已有落子则忽略
+    if state['board'][row][col] is not None:
+        return
 
-def tap(x, y):
-    """Draw X or O in tapped square."""
-    x = floor(x)
-    y = floor(y)
+    # 当前玩家落子
     player = state['player']
-    draw = players[player]
-    draw(x, y)
+    draw = drawx if player == 0 else drawo
+    draw(fx, fy)
     update()
-    state['player'] = not player
-
-
+    state['board'][row][col] = player
+
+    # 检查胜利
+    result = check_win()
+    if result is not None:
+        state['game_over'] = True
+        penup()
+        goto(0, 0)
+        color('green')
+        if result == 0:
+            write("You Win!", align='center', font=('Arial', 24, 'bold'))
+        elif result == 1:
+            write("Computer Wins!", align='center', font=('Arial', 24, 'bold'))
+        else:
+            write("Draw!", align='center', font=('Arial', 24, 'bold'))
+        return
+
+    # 切换玩家
+    state['player'] = 1 - player
+
+    # 如果轮到电脑，就随机落子
+    if state['player'] == 1:
+        _, move = minimax(True)       # True 表示电脑层 (maximizing)
+        r, c = move
+        # 计算该格左下角坐标
+        fx_ai = c*133 - 200
+        fy_ai = r*133 - 200
+        # 延迟一点，看起来更自然
+        ontimer(lambda: tap(fx_ai + 1, fy_ai + 1), 200)
+
+# 主流程
 setup(420, 420, 370, 0)
 hideturtle()
 tracer(False)
 grid()
 update()
 onscreenclick(tap)
-done()
+done()