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