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