Повернення до головоломок

Ось таке завдання: розставити на шахівниці мінімальна кількість тур так, щоб кожне поле було атаковано не менш, ніж 2-ма турами. Тура може атакувати через іншу човен і не атакує поле на якому стоїть.

Відповідь: Дванадцять як мінімум.

  1 2 3 4 5 6 7 8
  ___ ___ ___ ___ ___ ___ ___ ___
 h |  |  |  |  |  Л |  Л |  Л |  |
  --- --- --- --- --- --- --- ---
 g |  Л |  |  |  |  |  |  |  |
  --- --- --- --- --- --- --- ---
 f |  Л |  |  |  |  |  |  |  |
  --- --- --- --- --- --- --- ---
 e |  Л |  |  |  |  |  |  |  Л |
  --- --- --- --- --- --- --- ---
 d |  |  |  |  |  |  |  |  Л |
  --- --- --- --- --- --- --- ---
 c |  |  |  |  |  |  |  |  Л |
  --- --- --- --- --- --- --- ---
 b |  |  |  |  |  |  |  |  Л |
  --- --- --- --- --- --- --- ---
 a |  |  Л |  Л |  Л |  |  |  |  |
  --- --- --- --- --- --- --- ---