How to Solve Star Battle Puzzles

In this article, we will take a look at some strategies you can use to help you solve star battle puzzles, also sometimes just called 'stars'. In these puzzles, you are typically presented with a 10x10 grid and must place two stars in each row, column and bold-lined region that constitute the grid. Stars cannot touch, even diagonally. This means that any 2x2 region can have at most one star in it.

The rules are simple, however solving the puzzles may not be, particularly if you are new to the puzzle type. However, there are a range of strategies and techniques, from the simple to the fairly complicated, that can be used to help you make progress. There is quite a lot of depth to star battle puzzles, and with a good puzzle it shouldn't be a case of simply guessing at possible configurations, there should always be a way to make progress.

One of the best ways to start is to look at the smallest regions first, as these often bear fruit - either through instant placements of stars, or through helping you to rule in / out where stars can and cannot go in a region.

For instance, look at the start grid below:

You'll see that here we are looking at the smallest region in the puzzle, which contains only three squares. Since we know that each region must contain two stars, we can instantly place the stars in this region, since we know that the square that contains a red oval cannot contain a star. Why? Because if it did, it would mean neither of the other two squares in the region that neighbour it could contain a star, breaking the rule that there must be two stars in each region. So, whenever you have a region of just three squares in a standard star battle puzzle (where two stars must be placed in each region) you can instantly place the stars. Remember when you place stars to put an 'x' in every square that they neighbour, including squares that they neighbour diagonally.

Next, let's look at the only region in the puzzle that contains just four squares - the next smallest in the grid. Again we can see here that the square we have the red oval in cannot contain a star. That's because it would again mean we would no longer be able to place two stars in the region, since placing a star where the red oval is would mean that none of the neighbouring squares (marked here with yellow ovals) could also contain stars. The symmetry here also means that the same logic applies to the square directly underneath the one containing the red oval. Now that we have ruled out two of the four squares, there are only two left, and so we can place the two stars in the two squares in row one. This in turn means that the rest of the row one can be crossed off as we have also found both stars for that row now.

It is often the case that you won't be able to place stars exactly, but you will be able to rule squares in or out. Take a look at the region of five squares in the bottom row, plus one square in the penultimate row, that we have indicated above.

Note that the rule that there cannot be more than one star in any 2x2 mini-square region means that there must be one star in the region marked with the green line, and another in the region marked with the green/yellow line. We have marked with red ovals the squares that border the stars, no matter exactly where in those squares the stars are placed. This means that we can mark the squares that contain the red ovals with X's, as we know they cannot contain stars.

Particularly with harder puzzles it can be useful to consider multiple regions at once, and consider where the stars can go in those regions. If you take a look at the image above, you can see we have done that by considering column one and two together. Note that, as marked with the green rectangle, all the squares in column one and two belong to just two bold-lined regions. Since there must be two stars in each column, this means we know that the four stars for the first two columns must be shared by these two bold-lined regions, and therefore none of the other squares of those bold-lined regions in other columns can contain any stars. This means that we can put X's in the squares marked in red here. Although in this particular puzzle this wasn't necessary as we already knew the squares marked in red could not contain stars from the application of the logic in the first step above, in other puzzles this sort of thinking is very useful and indeed necessary to be able to make progress.

We hope you found these hints, tips and solving strategies for star battle useful. Do you like star battle puzzles? Perhaps you have other strategies that you like to use when solving them? Please do feel free to comment and let us know your thoughts on this fun puzzle type!
Date written: 02 Jun 2021

Category: logic puzzles | Keywords: star battle | logic puzzles | strategy

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