Question

I’m trying to write a little ship battle game in java.

It is 100% academic, I made it to practice recursion, so… I want to use it instead of iteration, even if it’s simpler and more efficient in most some cases.

Let’s get down to business. These are the rules:

• Ships are 1, 2 or 3 cells wide and are placed horizontally only.
• Water is represented with 0, non-hit ship cells are 1, hit ship cells are 2 and sunken ships have all it’s cells in 3.

With those rules set, I’m using the following array for testing:

int[][] board = new int[][]
{
    {0, 1, 2, 0, 1, 0},
    {0, 0, 1, 1, 1, 0},
    {0, 3, 0, 0, 0, 0},
    {0, 0, 2, 1, 2, 0},
    {0, 0, 0, 1, 1, 1},
};

It works pretty good so far, and to make it more user-friendly I would like to add a couple of reports. these are the methods I need for them:

1. Given the matrix, return the amount of ships in it.
2. Same as a), but separating them by state (amount of non-hit ships, hit and sunken ones).

I will need a hand with those reports, and I would like to get some ideas.

Remember it must be done using recursion, I want to understand this, and the only way to go is practice!

Thanks a lot for your time and patience :).

Answer 1

It’s not possible, unless you specify that ships must be separated by a 0. Otherwise, 1,1 could be a ship of length 2, or two ships of length 1.

Given that restraint, both of your reports could/should be done as a single process which turns a map into a list of ships.

I don’t terribly feel like writing out the recursive wrappers (I assume you know how to do “iterate” over an array using a recursive function), so I’m skipping that part.

1. loop over rows, because ships cannot span rows, they can be treated independently.
2. for each state-class ship data can be in (no ship, ship, sunk ship), have a function
3. This function checks if the next element
   1. Doesn’t exist
   2. Is the same as the current one (can be hardcoded by the different functions)
   3. Is different from the current one (go to the right one).
4. As you traverse the array, you assemble a list of ships.
5. You now have a list of ships, which you can count the length of, or do more complicated reports on

It may or may not be better to use a single function that isn’t hard-coded, but that seems a tad more difficult, and with only three options, hardcoding isn’t too much code-overhead (since all three do work somewhat differently).

Alternatively, you could use an entirely separate method, where by you iterate across the map counting “rising edges” of ships. This is a much lighter-weigh solution, but doesn’t afford you anywhere near as much flexibility in what you can do with the resulting data.

… By lighter weight, I mean “could be done using regex”