Fig 1]

[Illustration:

+---+---+---+---+---+

| | | | | |

*===*===*===*---+---+

| | | H | |

+---+---*===*---+---+

| | HHHHH | |

+---+---*===*---+---+

| | H | | |

+---+---*===*===*===*

| H | | | |

+---*---+---+---+---+

Amusements in Mathematics · 第 331 / 970 题