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requirements.txt

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+pygame

tictactoe.py

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+"""
+Tic Tac Toe Player
+"""
+
+import math
+
+X = "X"
+O = "O"
+EMPTY = None
+
+
+def initial_state():
+    """
+    Returns starting state of the board.
+    """
+    return [[EMPTY, EMPTY, EMPTY],
+            [EMPTY, EMPTY, EMPTY],
+            [EMPTY, EMPTY, EMPTY]]
+
+
+def player(board):
+    """
+    Returns player who has the next turn on a board.
+    """
+    x_count = sum(row.count(X) for row in board)
+    o_count = sum(row.count(O) for row in board)
+    return X if x_count == o_count else O
+
+
+def actions(board):
+    """
+    Returns set of all possible actions (i, j) available on the board.
+    """
+    return {(i, j) for i in range(3) for j in range(3) if board[i][j] == EMPTY}
+
+
+def result(board, action):
+    """
+    Returns the board that results from making move (i, j) on the board.
+    """
+    if board[action[0]][action[1]] is not EMPTY:
+        raise Exception("Invalid action")
+    
+    new_board = [row[:] for row in board]
+    new_board[action[0]][action[1]] = player(board)
+    return new_board
+
+
+def winner(board):
+    """
+    Returns the winner of the game, if there is one.
+    """
+    for line in board:  # Check rows
+        if line[0] == line[1] == line[2] and line[0] is not None:
+            return line[0]
+    for col in range(3):  # Check columns
+        if board[0][col] == board[1][col] == board[2][col] and board[0][col] is not None:
+            return board[0][col]
+    if board[0][0] == board[1][1] == board[2][2] and board[0][0] is not None:  # Check diagonal
+        return board[0][0]
+    if board[0][2] == board[1][1] == board[2][0] and board[0][2] is not None:  # Check anti-diagonal
+        return board[0][2]
+    return None
+
+
+def terminal(board):
+    """
+    Returns True if game is over, False otherwise.
+    """
+    return winner(board) is not None or all(cell is not EMPTY for row in board for cell in row)
+
+
+def utility(board):
+    """
+    Returns 1 if X has won the game, -1 if O has won, 0 otherwise.
+    """
+    win = winner(board)
+    if win == X:
+        return 1
+    elif win == O:
+        return -1
+    else:
+        return 0
+
+
+def minimax(board):
+    """
+    Returns the optimal action for the current player on the board.
+    """
+    if terminal(board):
+        return None
+
+    turn = player(board)
+
+    def max_value(board):
+        if terminal(board):
+            return utility(board), None
+        v = -math.inf
+        best_move = None
+        for action in actions(board):
+            val, _ = min_value(result(board, action))
+            if val > v:
+                v = val
+                best_move = action
+        return v, best_move
+
+    def min_value(board):
+        if terminal(board):
+            return utility(board), None
+        v = math.inf
+        best_move = None
+        for action in actions(board):
+            val, _ = max_value(result(board, action))
+            if val < v:
+                v = val
+                best_move = action
+        return v, best_move
+
+    if turn == X:
+        _, move = max_value(board)
+    else:
+        _, move = min_value(board)
+
+    return move
+
+