检查TicTacToe的获胜者？

def check_winner(board):
    # 检查每一行
    for row in board:
        if row[0] == row[1] == row[2] != '-':
            return row[0]

    # 检查每一列
    for col in range(3):
        if board[0][col] == board[1][col] == board[2][col] != '-':
            return board[0][col]

    # 检查对角线
    if board[0][0] == board[1][1] == board[2][2] != '-':
        return board[0][0]

    if board[0][2] == board[1][1] == board[2][0] != '-':
        return board[0][2]

    # 如果没有获胜者，返回空字符串
    return ''