PIENSALIA / SUDOKU EDUCATION

How to Solve Hard Sudoku

Hard Sudoku rewards a clean candidate workflow and verified deductions.

Level: Use a disciplined candidate workflow to solve hard Sudoku, from basic eliminations to X-Wing, Y-Wing, and Swordfish.

Prerequisites

Know the three Sudoku rules and keep candidates consistent across each row, column, and 3 × 3 box.

How to apply it

1. Scan the relevant units and write only legal candidates.
2. Compare the positions or candidates described by the technique.
3. Make one justified placement or elimination.
4. Update related notes and rescan for new singles.

Worked example

An X-Wing for one value can remove candidates from two columns and reveal a Hidden Single several steps later.

Common mistakes

• Guessing before checking every related unit.
• Leaving stale candidates after a placement.
• Applying a pattern without verifying all of its positions.

When to use it

Use this process for Expert and Extreme boards without turning an untested hypothesis into a placement.