a number puzzle with nine squares, each containing nine smaller squares, in which you have to put the numbers one to nine so that a number appears only once in each of the nine squares and in each row of nine across and down the puzzle 数独游戏（九个大方格中各有九个小方格，要求在空格中填数字一到九，且纵、横排各不重复） 
He passes the time doing sudokus. 他做数独游戏打发时间。 🔊🔊 There are sudokus at four levels of difficulty. 数独有四个难度级别。
