Star Battle › Guide
Star Battle Counting: Regions, Rows and Columns
If k unfinished regions in one-star Star Battle have all their available cells inside the same k rows, those regions use the rows' entire star capacity. Mark every other available cell in those rows empty. The same argument works with columns.
This is a counting or confinement deduction. It can prove empty cells before it locates a star. Count available cells after earlier exclusions, rather than requiring the full region shapes to fit inside the rows.
Why does matching capacity force empty cells?
Two unfinished regions each need one star, so together they need two. If every candidate lies in two rows, those rows must supply both stars. Each row can hold only one. A star elsewhere in either row would leave capacity for at most one of the two regions, which is impossible.
The rows need not be adjacent. The candidate cells do not need to form a rectangle, and a region may extend beyond the selected rows if its cells outside them are already excluded. Check that the source regions are unfinished and that you have included all their available cells.
These are real one-star practice checkpoints. Letters label regions, stars are placed pieces and dots are excluded cells. R1C1 is the top-left cell. The source links open the original boards; setup ledgers below explain the earlier marks.
1. 2 regions reserve 2 rows
region A, region B still need 2 stars altogether. Every candidate is in row 1, row 2, whose total capacity is 2 stars. Those capacities match.
| Region | Candidates | Stars still needed |
|---|---|---|
| region A | R1C1, R1C2, R1C4, R2C1 | 1 |
| region B | R1C5, R1C6, R2C6 | 1 |
Mark R2C3, R2C4 empty. These available cells lie in the reserved rows but outside the listed region candidates. No individual candidate becomes a star just because it is outlined.
Show the board after counting
Reconstruct the earlier marks
Apply each deduction in order. After placing a star, exclude its other row, column and region cells, plus all touching cells.
- A star at R2C2 would rule out every candidate in region C: exclude that cell.
- A star at R2C5 would rule out every candidate in region B: exclude that cell.
- A star at R1C3 would rule out every candidate in region C: exclude that cell.
- A star at R3C4 would rule out every candidate in region C: exclude that cell.
2. 2 regions reserve 2 columns
region A, region D still need 2 stars altogether. Every candidate is in column 5, column 6, whose total capacity is 2 stars. Those capacities match.
| Region | Candidates | Stars still needed |
|---|---|---|
| region A | R1C5, R1C6, R2C6 | 1 |
| region D | R3C5, R3C6, R4C5, R4C6 | 1 |
Mark R5C5, R6C5, R6C6 empty. These available cells lie in the reserved columns but outside the listed region candidates. No individual candidate becomes a star just because it is outlined.
Show the board after counting
Reconstruct the earlier marks
Apply each deduction in order. After placing a star, exclude its other row, column and region cells, plus all touching cells.
- A star at R2C3 would rule out every candidate in region C: exclude that cell.
- A star at R2C5 would rule out every candidate in region A: exclude that cell.
- A star at R4C4 would rule out every candidate in region C: exclude that cell.
- A star at R5C6 would rule out every candidate in region E: exclude that cell.
- A star at R6C4 would rule out every candidate in row 5: exclude that cell.
3. 3 regions reserve 3 rows
region D, region E, region F still need 3 stars altogether. Every candidate is in row 4, row 5, row 6, whose total capacity is 3 stars. Those capacities match.
| Region | Candidates | Stars still needed |
|---|---|---|
| region D | R4C1, R5C1, R6C1 | 1 |
| region E | R5C4, R5C5, R5C6, R6C6 | 1 |
| region F | R4C2, R5C3, R6C3, R6C4 | 1 |
Mark R4C3, R4C4, R4C5, R4C6 empty. These available cells lie in the reserved rows but outside the listed region candidates. No individual candidate becomes a star just because it is outlined.
Show the board after counting
Reconstruct the earlier marks
Apply each deduction in order. After placing a star, exclude its other row, column and region cells, plus all touching cells.
- A star at R2C2 would rule out every candidate in region A: exclude that cell.
- A star at R3C4 would rule out every candidate in region B: exclude that cell.
- A star at R5C2 would rule out every candidate in region D: exclude that cell.
- A star at R6C2 would rule out every candidate in region F: exclude that cell.
- A star at R1C1 would rule out every candidate in region D: exclude that cell.
- A star at R2C1 would rule out every candidate in region D: exclude that cell.
- A star at R3C1 would rule out every candidate in column 2: exclude that cell.
- A star at R2C3 would rule out every candidate in region A: exclude that cell.
- A star at R1C5 would rule out every candidate in row 2: exclude that cell.
- A star at R3C5 would rule out every candidate in row 2: exclude that cell.
- A star at R6C5 would rule out every candidate in region E: exclude that cell.
Does this work in two-star Star Battle?
Yes, but count the remaining star quotas. Two completely unfinished regions need four stars; two empty rows have capacity for four. If all those region candidates fit in those rows, other cells in the rows are empty. If some stars are already placed, subtract them from each unit's quota before comparing.
Candidate coverage alone does not establish that a two-star region can fit a valid pair: the no-touch rule still applies. A 2×2 block holds at most one star, even when four cells remain. These three diagrams demonstrate the one-star case; use the complete two-star walkthrough for checked pair reasoning.
Common counting mistakes
- Counting region area instead of its star quota.
- Overlooking an available cell outside the selected rows or columns.
- Including a region that already has its required star.
- Concluding which cell holds a star when the argument only excludes other cells.
- Transferring a one-star count directly to a partially solved two-star board.
Learn confinement, revisit Queens strategy, or read how the example puzzles are verified. The publisher's Star Battle rules explain the underlying quotas and no-touch constraint.