Pure genius!

Well played!

Correction: String.join does use the StringBuilder library, because StringJoiner uses StringBuilder under the hood. This means that String.join, StringJoiner, and StringBuilder are all O(n) optimal ways to concatenate strings, whereas the string concatenation operator + is O(n^2).

It should be mentioned that no matter how many times a ship was damaged we only get 0.5 point for each ship. And it's also unclear how to calculate points, for those having problems with figuring out points:

points = numberOfDamagedShips * 0.5 + numberOfSunkShips - notTouchedShips.

Indeed take a look at the formula for points: points = numberOfDamagedShips * 0.5 + numberOfSunkShips - notTouchedShips

Assuming instructions are stored in 2D array x and y point to a single instruction, v should be an integer and you are responsible to change the single instruction to v character counterpart. In java it would look like that: arr[y][x] = (char) v.

In case of "get" your task is to store on the stack v integer counterpart: stack.push( (int) arr[y][x])

Had a trouble too. Turns out I haven't assumed at the beginning that the default dierction is to the right.

In Java tests there's a problem with every even n except 2. It's beacause of one 1 in the wrong place. To bypass this bug just add the below code before return statement:

if(size % 2 == 0 && size > 2)
  arr[size / 2][size / 2 - 1] = 1;

Aaand for me ..........