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