Killer Sudoku Pro

Killer Sudoku represents the evolution of classic number puzzles. This implementation delivers a professional-grade experience with rigorous validation and optimized puzzle generation.

TECHNICAL SPECIFICATIONS:
• 9×9 grid with standard Sudoku constraints (row/column/box uniqueness)
• Cage partitioning algorithm generates 15-35 cages per puzzle
• Target sum constraints with intra-cage non-repetition rule
• Three calibrated difficulty tiers:
- Easy: 1-3 cell cages, 12 given cells
- Medium: 1-4 cell cages, 6 given cells
- Hard: 1-5 cell cages, 0 given cells (pure deduction)

VALIDATION ENGINE:
Real-time conflict detection monitors:
• Row duplicates (horizontal constraint)
• Column duplicates (vertical constraint)
• Box duplicates (3×3 region constraint)
• Cage duplicates (intra-cage uniqueness)
• Cage sum overflow (partial sum exceeds target)
• Cage sum mismatch (completed cage sum ≠ target)

PERFORMANCE METRICS:
• Puzzle generation: under 2 seconds (optimized backtracking algorithm)
• Auto-save: 500ms debounced writes to UserDefaults
• Undo stack: 100-step history with O(1) rollback
• Timer resolution: 1-second precision with pause/resume

USER INTERFACE DESIGN:
• Dashed cage boundaries with 2pt inset rendering
• Head cell displays target sum (smallest index in cage)
• Cage completion state: green overlay for correct sums
• Related cell highlighting (same row/column/box)
• Cage highlighting (all cells in selected cage)
• Note mode: 3×3 candidate grid per cell

ALGORITHMIC GUARANTEES:
• Every puzzle has exactly one valid solution
• Cage partitioning ensures logical solvability
• No guesswork required—pure deductive reasoning

Optimized for iOS 16+. 100% offline operation. Zero network dependencies.