For the last week, I've had two puzzle ideas stuck in my head since I finished the Paint By Numbers Sudoku. One of them was to finally do a Battleship Sudoku in a quality way, and that is the focus of this entry.
There are two ways I can imagine making such a puzzle. The first is to try to pack in ships to fill in some fixed number of squares in each row/box/column and then put numbers in the remaining squares. It turns out that this route is a little less interesting but I went forward on it anyway. I stumbled a little at the start, struggling to find some fleet of ships that would reasonably fit a grid. Its hard to pack (possibly impossible) a fleet with say 3 cruisers, 5 destroyers, and 8 battleships (27 total boat parts) into a sudoku grid using standard battleship packing rules. I decided though I could use a Mini-Fleet of 5 destroyers (2 unit ships) and 8 submarines (1 unit ships) for 18 total boat parts, and then give clues on the side of the grid as to how many ships can be seen in each direction. In these puzzles you must place 2 boat units in each row/box/column following battleship touching rules (edit: that is to say, ships cannot be immediately adjacent to each other, not even diagonally) with the numbers 1 through 7 in the remaining empty squares according to standard sudoku rules. Its an ok puzzle type, but it does not feel as much like a battleships puzzle as the second version below. My favorite of this type, which I'll call "Mini-Fleet Sudoku", is by far the rightmost puzzle.
(Note: All given numbers can be consider "sea" spaces and do not contain ships).
The other way to imagine doing a battleship sudoku is to fit a standard fleet of ships into the grid, but number the pieces of these ships so that they end up being part of a standard sudoku grid as well. The few givens that would be placed in the puzzle would be designed at times to help steer boats into particular spots/orientations, resolve non-unique boat placements, etc. Combining both battleship strategies and sudoku logic is therefore essential with this type. I came up with a few themed logical steps I wanted to try to embed in each puzzle, and made a few puzzles of varying difficulty that contained these steps. I'm really proud of this variation and hope the three that follow give you a sense of what the puzzle can be like. They are arranged in apparent increasing difficulty from left to right. I plan on making several more in the future.
To fully explain what your solution will look like: you will have a valid 9x9 sudoku grid with the digits 1 through 9 in each row/box/column. You will also have a fully "docked" fleet of battleships with the numbers on the ships matching exactly the numbers in the sudoku grid, and with boat segments obeying the outside constraints given for the puzzle. I would really appreciate your opinion on these battleship sudoku variants, but to me, the latter example comes pretty close to being like chocolate and peanut butter. They still feel like sudoku and still feel like battleships, but need a little bit of new logic from the other puzzle to get all the way through. From now on I will call this a "Battleship Sudoku" in contrast to the earlier "Mini-Fleet Sudoku". Enjoy!
(Note: Again, all given numbers in the grid can be considered "sea" spaces and do not contain ships).