例子2:
★         ★ ★ ★         ★         
★        ★  ★  ★        ★         
★       ★   ★   ★       ★         
★      ★    ★    ★      ★         
★     ★     ★     ★     ★         
★    ★      ★      ★    ★         
★   ★       ★       ★   ★         
★  ★        ★        ★  ★         
★ ★         ★         ★ ★         
★  ★        ★        ★  ★         
★   ★       ★       ★   ★         
★    ★      ★      ★    ★         
★     ★     ★     ★     ★         
★      ★    ★    ★      ★         
★       ★   ★   ★       ★         
★        ★  ★  ★        ★         
★         ★ ★ ★         ★         
★        ★  ★  ★        ★         
★       ★   ★   ★       ★         
★      ★    ★    ★      ★