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