How to solve Star Battle: two stars, no touching
5 min read ·
Star Battle is Queens with twice the stars: two in every row, every column and every outlined region, and still no two touching, not even diagonally. That one change makes the reasoning deeper, because you now track pairs instead of single pieces.
If you know Queens, every idea carries over. This guide adds the ones that are special to two stars.
The rules
- Exactly two stars in every row, every column and every outlined region.
- Stars never touch, not even at a corner.
- Boards are 8×8 and the classic 10×10; each has one solution.
A 2×2 block holds at most one star
Any two cells of a 2×2 block touch each other, so a 2×2 block can hold at most one star. That simple fact is the engine of Star Battle:
- A region can never be just a 2×2 block, since it couldn't hold two stars. So a region that's mostly a 2×2 block must put one star outside it.
- Cover a row pair with 2×2 blocks: two rows of a 10×10 board split into five blocks, and those two rows need four stars, so four of the five blocks get one star each.
Count regions against rows
The Queens counting rule doubles: if k regions fit entirely inside k rows, they use all 2k stars of those rows. Every other cell in those rows is empty. The same works with columns, and in reverse: if k rows lie entirely inside k regions, the rest of those regions is empty.
Placing a region's two stars
When a region has few cells left, list the ways two stars can sit in it without touching. Cells that appear in every way are stars; cells that appear in none are empty. A region squeezed into a line of four cells, for example, can only take its stars in cells 1 and 3, 1 and 4, or 2 and 4.
After placing a star, mark all eight neighbours. After placing a second star in a row, column or region, mark the rest of it.
A solving routine
- Mark the cells that touch every cell of a small region.
- Find groups of k regions inside k rows or columns.
- Split tight areas into 2×2 blocks and count the stars they must hold.
- List the two-star arrangements of nearly full regions.
- Mark around every star, and finish each line or region once it has two.
Practise
On Puzzimo, tap to mark a cell ✕ (tap again to clear), double-tap to place a star, and drag to mark many cells at once. A star where the solution has none counts as a mistake: it's shown and turned into a mark, and the third ends the round. The daily challenge is 8×8.
Frequently asked questions
Why can a 2×2 square hold only one star?
Every two cells of a 2×2 square touch, at least diagonally, and stars may not touch. So at most one star fits in any 2×2 square.
Is Star Battle harder than Queens?
Usually, yes. With two stars per row, column and region you track pairs of positions instead of single cells, and the counting arguments run over more rows at once.
Where should I start a 10×10 Star Battle?
With the smallest or most cramped regions, then with groups of regions that fit inside the same number of rows or columns. Splitting two rows into five 2×2 blocks helps when nothing else does.