### Dr. Sudoku Prescribes #45 – Battleships

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Theme: Just Try Two Find Us.

Rules: Standard Battleships rules.

Answer String: For each row from top-to-bottom, enter the number of the first column from the left where a ship segment appears. If the row is empty, enter 0. Enter these numbers as a single string with no separators.

Time Standard: Battleships Grandmaster = 1:45, Master = 2:45, Expert = 5:30

• TheSubro says:

1. I did it in 1:39.

2. Before I go celebrating though, the funny part is that I know that I only did it that quickly because I accidentally had thought that R4C10 was X’d out prematurely (I got me some old eyes), and it made other decisions that should have taken longer almost automatic. I realized my mistake about 15 seconds too late, but figured “WTF” – might as well keep going and see if it was accidentally correct. I am the Chauncy Gardener of the puzzle world today.

Thanks.

TheSubro

• skynet says:

10 : 26 s!

• Anuraag Sahay says:

1:38 on this one. I think it deserved only around 50 seconds.

• Aaron Chan says:

How do I unfavourite a puzzle? I pressed favourite on this by accident.

• drsudoku says:

Right now I believe the only option is to go to thegriddle.net, go to your profile page, and unfavorite over there. I mentioned your concern to David and he will see if he can build it directly into the widget above.

• This puzzle actually yields to two basic solving techniques covered by Tom in other posts: placing the battleship, and accounting for all submarines.

After inserting the obvious ship segments at C4, E6, and E8, we arrive at the following position [Legend: L/M/R/*/_/. = left, middle, right segments, generic-segment, water, empty] (I apologize in advance if the board doesn’t render correctly as monospaced — I’ll only know if it displays well after I submit this comment!):

`                        1      1 2 3 4 5 6 7 8 9 0    +--------------------- A  | . . . _ . . . . . .   3 B  | . . _ _ _ _ . . . .   4 C  | . . . * R _ . . . .   4 D  | . . _ _ _ _ _ _ _ .   1 E  | _ _ _ _ _ L M R _ _   3 F  | . . _ O _ _ _ _ _ .   2 G  | _ _ _ _ _ _ _ _ _ _   0 H  | . . . _ . _ . . . .   2 I  | _ _ _ _ _ _ _ _ _ _   0 J  | . . . _ . . . . . .   1`

`     2 2 2 2 2 2 2 2 2 2 `

There are only two places to put the battleship: C2-C5 and B7-B10. Inserting it at C2-C5 forces a second battleship at B7-B10, so the battleship goes in B7-B10.

Inserting obvious ship segments at J6 and H9 brings us to the critical position:

`                        1      1 2 3 4 5 6 7 8 9 0    +--------------------- A  | . . . _ . _ _ _ _ _   3 B  | _ _ _ _ _ _ L M M R   4 C  | . . . * R _ _ _ _ _   4 D  | . . _ _ _ _ _ _ _ .   1 E  | _ _ _ _ _ L M R _ _   3 F  | . . _ O _ _ _ _ _ .   2 G  | _ _ _ _ _ _ _ _ _ _   0 H  | . . . _ . _ _ _ * .   2 I  | _ _ _ _ _ _ _ _ _ _   0 J  | _ _ _ _ _ O _ _ _ _   1`

`     2 2 2 2 2 2 2 2 2 2 `

The insight need here, covered by Tom elsewhere, is that all four subs are accounted for: F4, J6, row F, and column 5. Since there can be no other submarines, H10 must be a ship segment (otherwise H9 would be a fifth submarine). From here the rest is trivial.

If I could make a request of the excellent solvers who post to this blog, it would be to share their solving logic and techniques where possible. Back in 2005 I posted the following on Raymond Chen’s “The Old New Thing” in a thread relating to the Freecell solitaire game, but the comment is equally relevant to Solitaire Battleship puzzles:

I don’t consider myself a compulsive person, but I find I keep coming back time and time again to FreeCell. I (like everyone else on planet Earth?) play FreeCell like I eat salted peanuts: I finish a board and plunge into the next one. One of these days I want to enjoy a FreeCell board like a good chess problem: recording my solution, sitting back, reviewing it to find a better solution, deriving heuristic rules for being a better solver (and all this while sipping a hot cup of tea / drinking a beer / enjoying a martini etc.).

Like solving a good chess problem, like cryptanalyzing a difficult cipher, IMHO the payback in solving these puzzles is honing your skills for the next puzzle. Just my \$0.02.

Another very enjoyable puzzle — thanks, Tom!