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