Hard Star Battle answer — April 12, 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. 3-cell region rule: Middle cell can't hold a star (row 3, column 6).
3. Region completion: 2 stars needed, 2 candidates (row 3, column 5).
4. Mark 7 cells adjacent to stars as X (row 2, column 4).
5. Region completion: 1 star needed, 1 candidate (row 3, column 7).
6. Mark 5 cells adjacent to stars as X (row 2, column 7).
7. Row 3 complete: Mark 4 remaining cells as X (row 3, column 1).
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 6, column 4).
9. 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).
10. Three candidates with two adjacent: Isolated candidate must hold a star (row 5, column 5).
11. Mark 3 cells adjacent to stars as X (row 5, column 4).
12. Column 5 complete: Mark 4 remaining cells as X (row 1, column 5).
13. Region completion: 1 star needed, 1 candidate (row 7, column 4).
14. Mark 4 cells adjacent to stars as X (row 6, column 3).
15. 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).
16. 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 2).
17. Three candidates with two adjacent: Isolated candidate must hold a star (row 2, column 3).
18. Mark 2 cells adjacent to stars as X (row 1, column 3).
19. Region completion: 2 stars needed, 2 candidates (row 1, column 6).
20. Mark 1 cell adjacent to stars as X (row 1, column 7).
21. Region completion: 1 star needed, 1 candidate (row 4, column 3).
22. Mark 3 cells adjacent to stars as X (row 4, column 2).
23. Column 3 complete: Mark 1 remaining cell as X (row 9, column 3).
24. Column completion: 1 star needed, 1 candidate (row 9, column 4).
25. Clump analysis (Column 2): candidate clumps can only just supply the remaining stars (row 6, column 1).
26. Region completion: 1 star needed, 1 candidate (row 9, column 2).
27. Mark 1 cell adjacent to stars as X (row 8, column 2).
28. Row 9 complete: Mark 4 remaining cells as X (row 9, column 6).
29. Blocking rule: a star here would touch every other open cell in its region, leaving no room for the region's second star (row 7, column 8).
30. Blocking rule: a star here would touch every other open cell in its region, leaving no room for the region's second star (row 7, column 6).
31. Column completion: 1 star needed, 1 candidate (row 8, column 6).
32. Mark 2 cells adjacent to stars as X (row 7, column 7).
33. Region completion: 1 star needed, 1 candidate (row 6, column 7).
34. Mark 3 cells adjacent to stars as X (row 5, column 7).
35. Column completion: 2 stars needed, 2 candidates (row 1, column 8).
36. Mark 2 cells adjacent to stars as X (row 1, column 9).
37. Row 1 complete: Mark 1 remaining cell as X (row 1, column 1).
38. Region completion: 1 star needed, 1 candidate (row 2, column 1).
39. Column completion: 1 star needed, 1 candidate (row 8, column 8).
40. Mark 2 cells adjacent to stars as X (row 7, column 9).
41. Region completion: 1 star needed, 1 candidate (row 6, column 9).
42. Mark 1 cell adjacent to stars as X (row 5, column 9).
43. Region completion: 1 star needed, 1 candidate (row 4, column 9).
44. Row 4 complete: Mark 1 remaining cell as X (row 4, column 1).
45. Row completion: 1 star needed, 1 candidate (row 5, column 1).
46. Mark 1 cell adjacent to stars as X (row 6, column 2).
47. Region completion: 1 star needed, 1 candidate (row 7, column 2).
48. Solved! Every row, column, and region has its two stars, none touching.