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How to Use Hidden Pairs in Sudoku: The Technique Most Players Overlook

Introduction

If Naked Pairs clean up visible candidates, Hidden Pairs reveal the hidden structure of a unit — and are essential for solving Medium to Hard puzzles without guessing.

This technique feels tricky at first, but once you understand it, Hidden Pairs become one of the most reliable solving tools.

This guide explains what Hidden Pairs are, how to detect them, and how to use them effectively. Mastering Hidden Pairs significantly improves your solving ability.

Key Points

Understanding these fundamentals helps you master Hidden Pairs:

Hidden Pairs = two numbers that can only appear in two cells: Unique restriction
They may be "hidden" inside larger candidate sets: Not immediately obvious
Common in boxes, rows, and columns: Work in all units
Removing other candidates unlocks progress: Powerful elimination
Ideal for Medium/Hard solving: Essential for intermediate puzzles

What Is a Hidden Pair?

A Hidden Pair is a Sudoku solving technique where two numbers in the same row, column, or box can only appear in two specific cells. A Hidden Pair happens when:

Two numbers

In the same row/column/box

Can only appear in two specific cells

Example in a row:

Cell1: {1, 4, 7}

Cell2: {1, 3, 7}

Cell3: {4, 7}

If numbers 4 and 7 appear only in Cell1 and Cell3, that's a Hidden Pair, even though those cells have extra candidates.

The trick:

Remove all other candidates except 4 and 7

This compression unlocks new deductions.

Hidden Pairs vs Naked Pairs

| Feature | Hidden Pairs | Naked Pairs | |---------|-------------|-------------| | What matches? | Two numbers appear only in two locations | Two cells have same candidates | | Appearance | Hidden inside larger sets | Explicitly visible | | Action | Remove extra candidates | Remove same numbers from other cells |

Hidden Pairs are more subtle but more powerful.

Where to Find Hidden Pairs

They commonly appear in:

Boxes: The 3×3 box is the richest place for Hidden Pairs, especially in Medium puzzles.

Rows: Look for numbers that appear only twice in notes.

Columns: Vertical pairs reveal themselves with cleaner pattern alignment.

How It Works (Step-by-Step)

Detecting Hidden Pairs requires systematic scanning:

Step 1: Turn on Notes Mode

You need candidate visibility. Notes are essential for spotting Hidden Pairs.

Step 2: Scan Each Number from 1 to 9

Not by cell — by number frequency.

For example, in a box:

5 appears in 3 cells

6 appears in 2 cells

8 appears in 2 cells

If 6 and 8 both appear only in the same two cells → Hidden Pair.

Step 3: Verify Pairing

Check if the numbers overlap precisely. Both numbers must appear in exactly the same two cells.

Step 4: Remove Extra Candidates

Compress each cell to just these two numbers. This creates a clean Naked Pair structure.

Step 5: Look for New Singles

Hidden Pairs often lead to immediate breakthroughs through eliminations.

Examples

Here are practical examples demonstrating Hidden Pairs:

Example A — Hidden Pair {3,9} in a Row

Row 6:

Cell1: {2,3,9}

Cell2: {3,9}

Cell3: {4,9}

Numbers 3 and 9 appear only in Cell1 & Cell2 → Hidden Pair.

Eliminate "2" from Cell1.

Example B — Hidden Pair {5,8} in a Box

Inside the top-left box:

Only two cells contain {5,8}. Remove other candidates from those two cells.

Example C — Hidden Pair Creates an Immediate Single

Removing extra candidates reveals {6} somewhere else in the row.

Common Mistakes

Checking cell-by-cell instead of number-by-number

Hidden Pairs can't be seen unless you scan by number.

Confusing with pointing pairs

Pointing pairs eliminate outside the box — Hidden Pairs do not.

Forgetting to clean candidates

Leaving extra candidates breaks the logic chain.

Summary

Hidden Pairs expose invisible structure inside Sudoku units, enabling powerful candidate elimination and unlocking deeper logic pathways.

Mastering Hidden Pairs is essential for solving Medium and Hard puzzles efficiently. This technique bridges basic and advanced solving methods.

❓ FAQ

Q1: Are Hidden Pairs hard to learn?

They seem complex but are easy with practice. Systematic scanning makes detection straightforward.

Q2: Should beginners learn this technique?

Yes — it's a natural next step after Singles. Essential for Medium+ progression.

Q3: Do Hidden Pairs appear in all puzzles?

Most Medium and Hard puzzles include several. Very common in intermediate puzzles.

Q4: Do I need Notes mode?

Absolutely. No Notes → no Hidden Pairs. Notes are essential for detection.

Q5: Are Hidden Pairs part of advanced solving?

They're intermediate but critical for harder puzzles. Foundation for advanced techniques.

Q6: What's the difference from Naked Pairs?

Hidden Pairs are buried in larger candidate sets; Naked Pairs are visibly identical. Hidden requires scanning by number.

Q7: Do they work in boxes?

Yes, boxes are especially rich in Hidden Pairs. Box-level detection is highly effective.

Q8: How many eliminations can Hidden Pairs create?

Often removes 4-6 candidates from the two cells, creating significant progress and revealing new patterns.

Ready to master Hidden Pairs? Start practicing with Notes Mode enabled today!

Try Hard Sudoku on SudokuGames.org | Learn More Techniques

Explore our technique guides to master intermediate strategies, practice with Hard Sudoku puzzles, and unlock Medium/Hard puzzles!