Star Battle strategy

Solving Star Battle is mostly about ruling cells out. You rarely find a star directly. You remove every place it can't be until one spot is left. All the techniques below are different ways of ruling cells out, and you should try them in this order, because the early ones are the quickest to spot.

1. Clear the neighbours

A star blocks all eight cells around it. Mark those cells straight away, or leave Auto-marks on and we will do it for you. Do the same when a row, column or region has all its stars: everything else in it is out.

Begin with the smallest regions. In a two-star puzzle, a three-cell region has to be a straight line with a star at each end, so you get two stars and a stack of ruled-out cells on the first move.

2. Count what's left

After each move, check the line or region you just touched. If it needs two stars and has two open cells left, both are stars. Remember that stars can't touch, so three open cells in a row with two stars needed means the two outer cells are stars and the middle one is out.

3. Lock the line

Look for a region whose open cells all sit in one row or column. Its stars have to land in that line, so they use up that line's stars. Every other cell in the line is out. This works in reverse as well: if a line's open cells all belong to one region, the rest of that region is out.

4. Find the shared block

Some cells are blocked no matter which way a region plays out. Picture each way the region could place its stars. If one cell outside the region touches a star in every version, that cell is out, even though you don't yet know which version is right.

5. Count across lines

This is the move that separates easy from hard, and it is worth learning properly. Take a group of neighbouring rows and add up how many stars they still need. Then look at the regions:

• If some regions sit entirely inside those rows and need exactly that many stars, those regions fill the rows. Every other cell in those rows is out.
• If all the open cells in those rows belong to regions that need exactly that many stars, those regions finish inside the rows. Their cells outside the rows are out.

For example, in a two-star puzzle, rows 1 and 2 need four stars together. If two regions fit completely inside rows 1 and 2, those two regions account for all four stars, and any other cell in those rows can be ruled out. The same works for columns, and for groups of three or four lines on bigger boards.

6. Use 2×2 blocks

Any 2×2 block holds at most one star, because any two of its cells touch. Split two neighbouring rows of a 10×10 board into five 2×2 blocks. Those rows need four stars, so four of the five blocks hold exactly one star each. This often tells you where a region must place its star, and it is the quickest way to spot tight spots on the board.

7. Follow a move through to its end

When nothing else works, pick one cell and ask what would happen if it held a star. Follow the consequences. If some row, column or region can no longer fit its stars, the cell can't be a star, and you have made real progress. This isn't guessing, since you are proving something about the cell before you commit. Only our hardest puzzles need it.

Which moves does each difficulty need?

Questions

What is the best way to start a Star Battle puzzle?

Start with the smallest regions. A small region has few places for its stars, so it often gives you a certain cell or rules out cells around it before you have placed anything.

How do you solve Star Battle without guessing?

Keep ruling cells out. Clear the neighbours of every star, count the open cells left in each line and region, look for regions locked into one line, then count across groups of lines. Every puzzle here can be finished this way.

Why can a 2×2 block hold only one star?

Any two cells in a 2×2 block touch each other, side by side or corner to corner. Two stars in the same block would touch, which the rules forbid.