Hard Star Battle answer — February 6, 2025

Full written solution

Every deduction from the walkthrough above, in order. Each technique is explained in the Star Battle strategy guide.

1. Starting position — the grid is split into regions (bold outlines). Each row, column, and region needs exactly two stars, and no two stars may touch.
2. 3-cell region rule: Middle cell can't hold a star (row 8, column 8).
3. Region completion: 2 stars needed, 2 candidates (row 7, column 8).
4. Mark 7 cells adjacent to stars as X (row 6, column 7).
5. Region completion: 1 star needed, 1 candidate (row 9, column 8).
6. Mark 2 cells adjacent to stars as X (row 9, column 7).
7. Column 8 complete: Mark 5 remaining cells as X (row 1, column 8).
8. Three candidates with two adjacent: Isolated candidate must hold a star (row 1, column 9).
9. Mark 1 cell adjacent to stars as X (row 2, column 9).
10. Two-option rule: Cell adjacent to both candidates (row 2, column 6).
11. Two-option rule: Cell adjacent to both candidates (row 3, column 6).
12. Blocking rule: a star here would touch every other open cell in its region, leaving no room for the region's second star (row 7, column 4).
13. Three candidates with two adjacent: Isolated candidate must hold a star (row 8, column 4).
14. Mark 7 cells adjacent to stars as X (row 7, column 3).
15. Region completion: 1 star needed, 1 candidate (row 6, column 4).
16. Mark 5 cells adjacent to stars as X (row 5, column 3).
17. Column 4 complete: Mark 4 remaining cells as X (row 1, column 4).
18. Three candidates with two adjacent: Isolated candidate must hold a star (row 3, column 5).
19. Mark 3 cells adjacent to stars as X (row 2, column 5).
20. Region completion: 1 star needed, 1 candidate (row 1, column 5).
21. Mark 1 cell adjacent to stars as X (row 1, column 6).
22. Row 1 complete: Mark 4 remaining cells as X (row 1, column 1).
23. Three candidates in a column: Middle cell can't hold a star (row 3, column 3).
24. Column completion: 2 stars needed, 2 candidates (row 2, column 3).
25. Mark 2 cells adjacent to stars as X (row 2, column 2).
26. Column completion: 1 star needed, 1 candidate (row 4, column 3).
27. Mark 2 cells adjacent to stars as X (row 4, column 2).
28. Clump analysis (Column 2): candidate clumps can only just supply the remaining stars (row 6, column 1).
29. Three candidates with two adjacent: Isolated candidate must hold a star (row 8, column 2).
30. Mark 2 cells adjacent to stars as X (row 7, column 2).
31. Region completion: 2 stars needed, 2 candidates (row 6, column 2).
32. Mark 1 cell adjacent to stars as X (row 5, column 1).
33. Region completion: 1 star needed, 1 candidate (row 9, column 6).
34. Mark 1 cell adjacent to stars as X (row 8, column 6).
35. Region completion: 1 star needed, 1 candidate (row 4, column 1).
36. Mark 1 cell adjacent to stars as X (row 3, column 1).
37. Region completion: 1 star needed, 1 candidate (row 2, column 1).
38. Row 2 complete: Mark 1 remaining cell as X (row 2, column 7).
39. Region completion: 1 star needed, 1 candidate (row 3, column 7).
40. Mark 1 cell adjacent to stars as X (row 4, column 7).
41. Row 3 complete: Mark 1 remaining cell as X (row 3, column 9).
42. Row 4 complete: Mark 1 remaining cell as X (row 4, column 9).
43. Region completion: 2 stars needed, 2 candidates (row 5, column 9).
44. Region completion: 1 star needed, 1 candidate (row 7, column 6).
45. Mark 1 cell adjacent to stars as X (row 6, column 6).
46. Column 6 complete: Mark 1 remaining cell as X (row 5, column 6).
47. Region completion: 1 star needed, 1 candidate (row 5, column 7).
48. Solved! Every row, column, and region has its two stars, none touching.