Tuesday 9 April 2013

logical deduction - Lots of ships in the battleship


We have enough amount of $2$x$2$ grid ships where you can put them on the $14$x$14$ grid battleship board. If this was a real battleship game, you could simply put $49$ of these $2$x$2$ grid ships into the board without any grid shared.



This time, you are going to put the ships one by one shown as the example below. Every time you put a ship, it cannot share more than 1 grid with other ships. That is, it must occupy at least three empty grids. In this case,



At most how many ships can you put into the board?



If this question was asked for $4$x$4$, the answer would be $5$ as shown below:


enter image description here


Here is the wrong way playing the game where you put the green ship, it shares two grid at the same time when you put it:


enter image description here



Answer



An obvious upper bound is




65, because each new ship after the first must occupy at least empty 3 squares, and $1 + \frac{196 - 4}{3} = 65$.



I couldn't do that well, however, so this might be suboptimal. My best arrangement so far gets to



64 ships:

enter image description here



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