Hard Star Battle answer — April 13, 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 7).
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 8).
4. Three candidates with two adjacent: Isolated candidate must hold a star (row 7, column 7).
5. Mark 6 cells adjacent to stars as X (row 6, column 6).
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 8, 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 8, column 3).
8. Three candidates with two adjacent: Isolated candidate must hold a star (row 7, column 3).
9. Mark 6 cells adjacent to stars as X (row 6, column 2).
10. Row 7 complete: Mark 3 remaining cells as X (row 7, column 1).
11. Clump analysis (Region 2): candidate clumps can only just supply the remaining stars (row 3, column 8).
12. Three candidates with two adjacent: Isolated candidate must hold a star (row 6, column 9).
13. Two-option rule: Cell adjacent to both candidates (row 9, column 8).
14. Region completion: 1 star needed, 1 candidate (row 9, column 7).
15. Mark 1 cell adjacent to stars as X (row 9, column 6).
16. Column 7 complete: Mark 5 remaining cells as X (row 1, column 7).
17. Clump analysis (Column 6): candidate clumps can only just supply the remaining stars (row 2, column 5).
18. Clump analysis (Column 8): candidate clumps can only just supply the remaining stars (row 1, column 9).
19. Clump analysis (Column 8): each clump must supply its full share of stars (row 4, column 8).
20. Mark 1 cell adjacent to stars as X (row 4, column 9).
21. Two-option rule: Cell adjacent to both candidates (row 5, column 5).
22. Clump analysis (Region 5): candidate clumps can only just supply the remaining stars (row 6, column 1).
23. Row completion: 1 star needed, 1 candidate (row 6, column 5).
24. Mark 2 cells adjacent to stars as X (row 5, column 4).
25. Region completion: 1 star needed, 1 candidate (row 4, column 6).
26. Mark 2 cells adjacent to stars as X (row 3, column 5).
27. Row 4 complete: Mark 4 remaining cells as X (row 4, column 1).
28. Three candidates in a row: Middle cell can't hold a star (row 5, column 2).
29. Row completion: 2 stars needed, 2 candidates (row 5, column 1).
30. Row completion: 1 star needed, 1 candidate (row 5, column 3).
31. Region complete: Mark 2 remaining cells as X (row 8, column 1).
32. Row completion: 2 stars needed, 2 candidates (row 8, column 5).
33. Mark 2 cells adjacent to stars as X (row 9, column 4).
34. Row completion: 1 star needed, 1 candidate (row 8, column 9).
35. Mark 1 cell adjacent to stars as X (row 9, column 9).
36. Column 3 complete: Mark 4 remaining cells as X (row 1, column 3).
37. Region completion: 1 star needed, 1 candidate (row 9, column 2).
38. Column 5 complete: Mark 1 remaining cell as X (row 1, column 5).
39. Three candidates in a column: Middle cell can't hold a star (row 2, column 4).
40. Column completion: 2 stars needed, 2 candidates (row 1, column 4).
41. Column completion: 1 star needed, 1 candidate (row 3, column 4).
42. 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).
43. Three candidates with two adjacent: Isolated candidate must hold a star (row 1, column 1).
44. Mark 2 cells adjacent to stars as X (row 1, column 2).
45. Region completion: 1 star needed, 1 candidate (row 2, column 6).
46. Mark 1 cell adjacent to stars as X (row 1, column 6).
47. Row 1 complete: Mark 1 remaining cell as X (row 1, column 8).
48. Region completion: 1 star needed, 1 candidate (row 2, column 8).
49. Column 1 complete: Mark 1 remaining cell as X (row 3, column 1).
50. Region completion: 1 star needed, 1 candidate (row 3, column 2).
51. Solved! Every row, column, and region has its two stars, none touching.