Hard Star Battle answer — February 11, 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. Blocking rule: a star here would touch every other open cell in its region, leaving no room for the region's second star (row 8, column 8).
3. Blocking rule: a star here would touch every other open cell in its region, leaving no room for the region's second star (row 2, column 8).
4. Clump analysis (Region 3): candidate clumps can only just supply the remaining stars (row 4, column 6).
5. Three candidates with two adjacent: Isolated candidate must hold a star (row 8, column 1).
6. Mark 5 cells adjacent to stars as X (row 7, column 1).
7. Region completion: 1 star needed, 1 candidate (row 6, column 1).
8. Mark 1 cell adjacent to stars as X (row 6, column 2).
9. Column 1 complete: Mark 4 remaining cells as X (row 1, column 1).
10. Blocking rule: a star here would touch every other open cell in its region, leaving no room for the region's second star (row 3, column 3).
11. Clump analysis (Row 4): candidate clumps can only just supply the remaining stars (row 3, column 2).
12. Three candidates with two adjacent: Isolated candidate must hold a star (row 2, column 4).
13. Mark 5 cells adjacent to stars as X (row 1, column 3).
14. Clump analysis (Row 3): candidate clumps can only just supply the remaining stars (row 2, column 6).
15. Row completion: 1 star needed, 1 candidate (row 2, column 2).
16. Mark 1 cell adjacent to stars as X (row 1, column 2).
17. Column completion: 1 star needed, 1 candidate (row 4, column 2).
18. Mark 1 cell adjacent to stars as X (row 4, column 3).
19. Three candidates with two adjacent: Isolated candidate must hold a star (row 3, column 7).
20. Mark 2 cells adjacent to stars as X (row 3, column 6).
21. Row completion: 1 star needed, 1 candidate (row 3, column 9).
22. Clump analysis (Row 4): candidate clumps can only just supply the remaining stars (row 6, column 4).
23. Two last candidates (row 6): Eliminate 1 cell adjacent to both (row 7, column 4).
24. Clump analysis (Column 3): candidate clumps can only just supply the remaining stars (row 8, column 4).
25. Column completion: 1 star needed, 1 candidate (row 4, column 4).
26. Mark 1 cell adjacent to stars as X (row 4, column 5).
27. Clump analysis (Column 5): candidate clumps can only just supply the remaining stars (row 7, column 6).
28. Column completion: 2 stars needed, 2 candidates (row 1, column 6).
29. Mark 1 cell adjacent to stars as X (row 1, column 7).
30. Column completion: 1 star needed, 1 candidate (row 5, column 6).
31. Mark 2 cells adjacent to stars as X (row 5, column 7).
32. Row completion: 1 star needed, 1 candidate (row 6, column 3).
33. Mark 1 cell adjacent to stars as X (row 7, column 3).
34. Column completion: 1 star needed, 1 candidate (row 8, column 7).
35. Mark 2 cells adjacent to stars as X (row 7, column 8).
36. Row completion: 2 stars needed, 2 candidates (row 7, column 5).
37. Mark 1 cell adjacent to stars as X (row 8, column 5).
38. Region completion: 1 star needed, 1 candidate (row 9, column 5).
39. Row completion: 1 star needed, 1 candidate (row 7, column 9).
40. Mark 1 cell adjacent to stars as X (row 8, column 9).
41. Region complete: Mark 1 remaining cell as X (row 9, column 9).
42. Row 8 complete: Mark 1 remaining cell as X (row 8, column 3).
43. Region completion: 1 star needed, 1 candidate (row 9, column 3).
44. Column completion: 2 stars needed, 2 candidates (row 1, column 8).
45. Mark 1 cell adjacent to stars as X (row 1, column 9).
46. Column completion: 1 star needed, 1 candidate (row 5, column 8).
47. Mark 1 cell adjacent to stars as X (row 5, column 9).
48. Solved! Every row, column, and region has its two stars, none touching.