Hard Star Battle answer — April 9, 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 6, column 8).
3. Three candidates with two adjacent: Isolated candidate must hold a star (row 7, column 8).
4. Mark 7 cells adjacent to stars as X (row 6, column 7).
5. Region completion: 1 star needed, 1 candidate (row 5, column 9).
6. Mark 3 cells adjacent to stars as X (row 4, column 8).
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 1, column 2).
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 2, column 2).
9. Three candidates with two adjacent: Isolated candidate must hold a star (row 2, column 3).
10. Mark 6 cells adjacent to stars as X (row 1, column 3).
11. Clump analysis (Region 4): candidate clumps can only just supply the remaining stars (row 2, column 8).
12. 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 6).
13. Three candidates with two adjacent: Isolated candidate must hold a star (row 2, column 5).
14. Mark 4 cells adjacent to stars as X (row 1, column 5).
15. Row 2 complete: Mark 3 remaining cells as X (row 2, column 1).
16. Region completion: 1 star needed, 1 candidate (row 1, column 1).
17. Region completion: 1 star needed, 1 candidate (row 3, column 7).
18. Mark 3 cells adjacent to stars as X (row 3, column 8).
19. Clump analysis (Row 1): each clump must supply its full share of stars (row 3, column 9).
20. Row 3 complete: Mark 1 remaining cell as X (row 3, column 1).
21. Column 9 complete: Mark 2 remaining cells as X (row 1, column 9).
22. Blocking rule: a star here would touch every other open cell in its region, leaving no room for the region's second star (row 9, column 7).
23. Three candidates with two adjacent: Isolated candidate must hold a star (row 9, column 8).
24. Column 8 complete: Mark 1 remaining cell as X (row 1, column 8).
25. Region completion: 1 star needed, 1 candidate (row 1, column 7).
26. Column 7 complete: Mark 1 remaining cell as X (row 5, column 7).
27. Two-option rule: Cell adjacent to both candidates (row 8, column 5).
28. Two-option rule: Cell adjacent to both candidates (row 9, column 5).
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 9, column 3).
30. Three candidates with two adjacent: Isolated candidate must hold a star (row 9, column 2).
31. Mark 4 cells adjacent to stars as X (row 8, column 1).
32. Row completion: 2 stars needed, 2 candidates (row 8, column 4).
33. Mark 4 cells adjacent to stars as X (row 7, column 3).
34. Row completion: 1 star needed, 1 candidate (row 8, column 6).
35. Mark 2 cells adjacent to stars as X (row 7, column 6).
36. 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 5).
37. 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 3).
38. Two last candidates (row 7): Eliminate 2 cells adjacent to both (row 6, column 1).
39. Two last candidates (column 3): Eliminate 2 cells adjacent to both (row 5, column 2).
40. 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 6).
41. Row completion: 1 star needed, 1 candidate (row 5, column 1).
42. Mark 2 cells adjacent to stars as X (row 4, column 1).
43. Column 1 complete: Mark 1 remaining cell as X (row 7, column 1).
44. Region completion: 1 star needed, 1 candidate (row 7, column 2).
45. Mark 1 cell adjacent to stars as X (row 6, column 3).
46. Column completion: 1 star needed, 1 candidate (row 4, column 3).
47. Mark 1 cell adjacent to stars as X (row 4, column 4).
48. Region completion: 1 star needed, 1 candidate (row 6, column 4).
49. Mark 1 cell adjacent to stars as X (row 6, column 5).
50. Region completion: 2 stars needed, 2 candidates (row 4, column 5).
51. Region completion: 1 star needed, 1 candidate (row 6, column 6).
52. Solved! Every row, column, and region has its two stars, none touching.