Star Battle Solver, Step by Step
How to use the Star Battle solver
Choose the grid size and how many stars go in each row, column and region: two on a 10 by 10 is the classic. Pick a colour and paint each region of your puzzle by dragging across its squares. Press Explain the next step: the solver places the stars that are certain and crosses out squares that cannot have one, highlights the region, row or column the reason is about, and says why. Show the answer fills it in at once and checks the solution is the only one.
The rules of Star Battle
The grid is divided into as many regions as it has rows. Place stars so that every row, every column and every region holds exactly the same number of them, usually one or two, and no two stars touch, not even at a corner. With one star the puzzle is the same as the Queens puzzle.
How to solve Star Battle, step by step
Fit the stars into small regions. A region that needs two stars that cannot touch often has only a few ways to hold them; squares used by every way get a star, and squares used by none are crossed out. Squeeze regions into rows. When some regions have all their open squares inside the same number of rows, those rows' stars all go to them, so the rest of those rows is empty. The same works for columns, and the other way round, rows that lie inside as many regions. Check what a star would block. A square whose star would leave a nearby region or row with no room is crossed out. When those run out, the solver follows a star's consequences a few moves further and crosses it out if they lead to a dead end.
How it was checked
With one star, its count of solutions matched our Queens solver on 60 random grids; with two stars it matched a separate brute-force search on 40 more. On 29 generated puzzles from 6 by 6 to 12 by 12, every step it explained was checked against the answer: it never placed a wrong star or crossed out a right one.
More logic puzzles
The Queens puzzle solver handles the one-star version with the same moves, and the eight queens puzzle is the chess problem behind it. The nurikabe solver and the light up solver explain their steps the same way. For a puzzle you hold in your hands, see our brain teasers. There are more solvers on the puzzle tools page.
Frequently Asked Questions
How do you solve a Star Battle puzzle?
Start with the small regions: two stars that cannot touch often fit only a few ways, so squares used by every way get a star and squares used by none are crossed out. Then look for regions squeezed into as many rows or columns, which use up those rows, and cross out any square whose star would leave a neighbour with no room.
What are the rules of Star Battle?
Place stars so every row, every column and every region has the same number of them, usually one or two, and no two stars touch, not even diagonally.
Is Star Battle the same as the Queens puzzle?
The Queens puzzle is a one-star Star Battle: one per row, column and region, none touching. Two-star puzzles on a 10 by 10 grid are the classic Star Battle.
Can two stars in a Star Battle touch diagonally?
No. Stars never touch at all, so every square around a star, corners included, is empty.
Does every Star Battle have one solution?
A well-made one does. The solver checks, and says if the regions you painted allow more than one.