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