DIFFICULTY · HARD
Hard Sudoku
Hard puzzles are for experienced solvers ready for layered eliminations. Accurate candidate notes become essential because progress may not create an immediate placement.
Who Hard is for
Choose Hard when pairs and locked candidates are familiar and you can maintain a clean candidate grid.
Techniques to practise
Search for hidden pairs, naked and hidden triples, box-line reduction, pointing pairs and early X-Wing patterns.
How to recover when stuck
Audit each digit across all nine boxes, then inspect houses with the fewest unresolved candidates. Recheck pairs before moving to advanced patterns.
Check every deduction
A single incorrect candidate removal can derail a long solve. Confirm the pattern and every affected row, column and box.
Medium versus Hard
Medium usually resolves with compact local logic. Hard more often combines multiple eliminations before a new value becomes certain.