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Solving Battleship: (Outside Sums)

This is a nice technique to use while solving Battleship puzzles. You may not always find it useful directly, but it comes in handy in parts when used correctly.

Take a look at Puzzle No.12

If you cannot start this puzzle without a guess, it has to be because you are not aware of this technique :-)

Take a look at the numbers outside the grid. The total of the right-side numbers is 20. The total of the bottom numbers is also 20. The total cells occupied by ships is 20 ( 1 x 4 + 2 x 3 + 3 x 2 + 4 x 1 ). Hence, even though the blank rows/columns can be any number, they have to be zero! The cells marked in red indicate it cannot be a ship.

Using the standard rules, you should easily be able to complete the puzzle.

This technique can be used effectively when the given sums are very low or very high. If the sum of numbers is 18, the blank row/column has to have just 2 cells with ships and so on...

Other Solving Techniques


Tejal Phatak said...

Superb! said...

hmm... I totally don't understand what you mean. Of course sum on right is same as on bottom and is same as number of ship cells... it is always like that, or? But from next sentence I am totally confused: "blank rows can be any number, they have to be zero" ???

Rohan Rao said...

In rows/columns that no number is given outside, it does not mean there are no cells containing ships. Those rows/columns can contain one or more cells with ships.

In the example above, they have to be zero, since the 20 cells are covered in the givens.

I hope it is clear now. said...

yes thanks, now it is clear... i am new to those puzzles and i tough no number is same as zero

Unknown said...

ah did not know that, now i know why i always don't complete it in the Evening Standard!! Cheers