Su Doku Strategies: Common Patterns and How to Spot Them

Su Doku for Beginners: Step-by-Step Solving Guide

Su Doku is a logic-based number-placement puzzle that sharpens concentration and reasoning. This guide teaches the fundamentals and gives a clear, repeatable process to solve standard 9×9 puzzles.

What Su Doku is

• Grid: 9×9 cells divided into nine 3×3 blocks.
• Goal: Fill every cell with digits 1–9 so that each row, column, and 3×3 block contains each digit exactly once.
• Given numbers: Some cells start filled; these are clues.

Basic notation and helpful habits

• Scan: Look across rows, columns, and blocks to eliminate possibilities.
• Pencil marks: Write small candidate numbers in empty cells, then erase as you eliminate possibilities.
• One-step logic: Start with obvious fills before using advanced techniques.
• Work systematically: Progress left-to-right, top-to-bottom or focus on the most constrained row/column/block.

Step-by-step solving process

1. Identify easy fills (Singles)

• Find any cell with only one possible digit (based on existing digits in its row, column, and block). Fill those first.

2. Complete obvious cells in rows/columns/blocks (Hidden Singles)

• Inside a row, column, or block, if a digit can only go in one cell (even if that cell currently has multiple candidates), place it there.

3. Use Candidate Elimination (Naked Pairs / Triples)

• If two cells in a unit (row/column/block) share the exact same two candidates, those two digits can be removed from other cells in that unit. Extend the idea to triples when three cells share the same three candidates.

4. Block–Row / Block–Column interactions (Pointing)

• If within a 3×3 block a candidate digit can only appear in one row (or column) of that block, you can eliminate that digit from the rest of that row (or column) outside the block.

5. X-Wing (basic fish technique)

• For an advanced-but-common technique: if two rows each have a candidate digit in exactly the same two columns, then that digit must be in those two columns, allowing elimination of that digit from other cells in those columns.

6. Continue alternating scanning and elimination

• After applying a technique, update pencil marks and repeat simpler scans (Singles and Hidden Singles) — these often appear after eliminations.

7. When stuck, use trial & backtrack (last resort)

• Choose a cell with two candidates, tentatively place one candidate and continue solving. If you reach a contradiction, undo and try the other candidate. Use sparingly — most beginner puzzles don’t require guessing.

Practical solving tips

• Start with blocks: Beginners often find scanning 3×3 blocks first yields quick placements.
• Keep candidates tidy: Use consistent small handwriting or an app’s pencil-mark feature.
• Work the whole grid: Avoid focusing on a single area too long; progress elsewhere often unlocks stuck areas.
• Practice different techniques: Start with Singles, Hidden Singles, and Pointing; add Naked Pairs and X‑Wing later.
• Set a time goal: Begin with untimed solving to learn patterns, then time yourself to track improvement.

Common beginner mistakes to avoid

• Filling without checking all three constraints (row, column, block).
• Forgetting to update or erase candidates after fills.
• Guessing too early instead of exhausting logical techniques.

Example walkthrough (brief)

• Given a cell in row 2 that cannot contain {1,2,4,6,7,8,9} because those appear in its row/column/block, the only candidate is 3 — place 3 (Single).
• In block 5, if 5 can only appear in one cell of that block though other candidates exist there, place 5 (Hidden Single).
• If two cells in row 7 both show candidates {2,9} and no other cell in that row contains 2 or 9 as a candidate, remove 2 and 9 from other cells in that row (Naked Pair).

Practice progression

• Start with easy puzzles (labeled “Easy” or “Beginner”) to master Singles and Hidden Singles.
• Move to “Medium” to practice Naked Pairs and Pointing.
• Try “Hard” only after you’re comfortable with advanced patterns like X‑Wing.

Quick reference checklist

• Scan for Singles → Find Hidden Singles → Update candidates → Look for Naked Pairs/Triples → Apply Block–Row/Column pointing → Try X‑Wing or similar patterns → Resort to trial only if necessary.

Practice consistently and your speed and pattern recognition will improve quickly. Enjoy solving!