Daily logic puzzle
Star Battle online, a new garden every midnight.
Star Battle is a grid puzzle where you place a fixed number of stars in every row, every column and every outlined region, and no two stars may touch. Ours is called Hedgehogs, it is free, there is no account and no advertising, and a new one appears at midnight.
- a new puzzle at midnight, easy on Monday and hardest on Sunday
- exactly one solution, and a program proves it before the puzzle is published
- hints that explain the technique, a two step Check, no red ink while you play
Today's garden. The hedgehogs are the stars, the coloured flowerbeds are the regions.
The rules
Three rules, and that is the whole game.
Star Battle is usually played as two stars per row; ours is the two star version on a nine by nine grid.
- Two hedgehogs go in every row, in every column and in every flowerbed. The flowerbeds are the outlined shapes, and a garden with nine rows has nine columns and nine flowerbeds, so eighteen hedgehogs in all.
- No two hedgehogs may touch, not side by side and not diagonally. Every hedgehog keeps the eight cells around it empty.
- Exactly one arrangement fits. Mark the cells you have ruled out however you like; only the hedgehogs count.
Our name for it
We call it Hedgehogs.
The puzzle is known as Star Battle, sometimes as Two Not Touch. We give every game an animal name because the rule that makes it work reads better as a story: hedgehogs prickle, so no two of them will sit next to each other, not even corner to corner. That is the no touching rule, and nobody has to memorise it.
Nothing else changes. If you have solved Star Battle elsewhere, everything you know applies here, down to the technique of ruling out whole rows once a region is full.
Where to start
Three ways in.
The archive of past gardens is free as well and goes back a year: Hedgehogs archive.
- Play today's garden
The daily puzzle, easy on Monday and hardest on Sunday, new at midnight.
- How to play Star Battle
The rules with a worked example, the keyboard controls and the solving techniques.
- Practice sets
Sets by difficulty when one puzzle a day is not enough.
One solution
A program says so, not a person.
Every puzzle we publish has exactly one solution, and it is a program that decides. The generator throws a candidate away unless the solver returns exactly one solution and unless a second solver, restricted to human style reasoning, finishes it without guessing.
You can see the check yourself: the file tests.mjs in the game folder runs it over thirty days in every size. That is why you will never need to try a hedgehog to see whether the grid falls apart twenty moves later.
While you play, nothing goes red. A mistake is shown only by Check, in two steps: first how many cells are wrong and roughly where, then which ones. Hint works the same way, first the technique and the place, then the move. Both are free and unlimited, and the timer is a score, never a limit.
Questions
Questions about Star Battle.
Is Star Battle free here?
Yes. The daily puzzle, the practice sets, the archive going back a year, the hints and the Check are all free, with no account and no advertising. We sell printable puzzle books on the same site, and that is the whole business model.
How many stars go in each row?
Two, in this version. Star Battle exists in one star, two star and three star variants; ours is the two star kind on a nine by nine grid with nine outlined flowerbeds, so eighteen stars in all. The rule is the same for rows, columns and regions.
Can two stars touch diagonally?
No. That is the rule people trip over most often. A star keeps all eight surrounding cells empty, so corner to corner counts as touching. It is also the most useful rule when solving, because one placed star rules out eight cells at once.
Do I need to guess anywhere?
No, and that is checked rather than promised. Every published puzzle was solved by a program restricted to reasoning, without trial and error, before it was allowed out. If you find yourself guessing, there is a deduction you have not spotted; Hint will name the technique and the place before it shows you the move.
Does it work on a phone?
Yes. The grid scales to the screen and you place and remove hedgehogs by tapping. Everything runs in your browser, there is nothing to install and nothing to sign up for.
Where can I get more of these on paper?
In the Hedgehogs book: one hundred Star Battle puzzles as a printable PDF in A4 and US Letter, with the solutions at the back. There is a free five puzzle sample to look at first. See the <a href="/puzzle-books/star-battle-puzzle-book/">Star Battle puzzle book</a>.
Related
More of the same.
One hundred of these on paper, with the solutions at the back: Star Battle puzzle book (PDF, free sample).
All ten daily games are on one page: daily logic games.
Auf Deutsch: Star Battle online spielen.