Hard Star Battle answer — June 29, 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 8, column 9).
4. Three candidates with two adjacent: Isolated candidate must hold a star (row 9, column 9).
5. Mark 1 cell adjacent to stars as X (row 9, column 8).
6. Two-option rule: Cell adjacent to both candidates (row 6, column 8).
7. Two-option rule: Cell adjacent to both candidates (row 6, column 9).
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 5, column 7).
9. Clump analysis (Region 1): candidate clumps can only just supply the remaining stars (row 5, column 4).
10. Three candidates with two adjacent: Isolated candidate must hold a star (row 5, column 6).
11. Mark 5 cells adjacent to stars as X (row 4, column 5).
12. Three candidates with two adjacent: Isolated candidate must hold a star (row 6, column 4).
13. Mark 3 cells adjacent to stars as X (row 5, column 3).
14. Two-option rule: Cell adjacent to both candidates (row 8, column 6).
15. Two-option rule: Cell adjacent to both candidates (row 8, column 7).
16. Two-option rule: Cell adjacent to both candidates (row 4, column 9).
17. Two-option rule: Cell adjacent to both candidates (row 5, column 9).
18. Two last candidates (row 6): Eliminate 4 cells adjacent to both (row 5, column 1).
19. Row completion: 1 star needed, 1 candidate (row 5, column 8).
20. Mark 1 cell adjacent to stars as X (row 4, column 8).
21. Clump analysis (Row 4): candidate clumps can only just supply the remaining stars (row 3, column 1).
22. Clump analysis (Row 3): candidate clumps can only just supply the remaining stars (row 2, column 6).
23. Clump analysis (Row 8): candidate clumps can only just supply the remaining stars (row 9, column 2).
24. Clump analysis (Region 9): candidate clumps can only just supply the remaining stars (row 2, column 3).
25. Three candidates with two adjacent: Isolated candidate must hold a star (row 2, column 7).
26. Mark 4 cells adjacent to stars as X (row 1, column 6).
27. Region completion: 2 stars needed, 2 candidates (row 3, column 5).
28. Mark 1 cell adjacent to stars as X (row 4, column 4).
29. Region completion: 1 star needed, 1 candidate (row 3, column 9).
30. Column completion: 1 star needed, 1 candidate (row 7, column 8).
31. Mark 2 cells adjacent to stars as X (row 7, column 7).
32. Region completion: 1 star needed, 1 candidate (row 7, column 6).
33. Mark 1 cell adjacent to stars as X (row 8, column 5).
34. Column 6 complete: Mark 1 remaining cell as X (row 9, column 6).
35. Column completion: 1 star needed, 1 candidate (row 9, column 7).
36. Row 9 complete: Mark 3 remaining cells as X (row 9, column 1).
37. Region completion: 1 star needed, 1 candidate (row 8, column 2).
38. Mark 2 cells adjacent to stars as X (row 8, column 1).
39. Row completion: 1 star needed, 1 candidate (row 8, column 4).
40. Column completion: 2 stars needed, 2 candidates (row 1, column 3).
41. Mark 2 cells adjacent to stars as X (row 1, column 4).
42. Region completion: 1 star needed, 1 candidate (row 2, column 1).
43. Region completion: 1 star needed, 1 candidate (row 1, column 5).
44. Column completion: 1 star needed, 1 candidate (row 4, column 3).
45. Mark 1 cell adjacent to stars as X (row 4, column 2).
46. Region completion: 1 star needed, 1 candidate (row 4, column 1).
47. Column 1 complete: Mark 1 remaining cell as X (row 6, column 1).
48. Region completion: 1 star needed, 1 candidate (row 6, column 2).
49. Solved! Every row, column, and region has its two stars, none touching.