Hidden Triples & Quads

Find Candidates Hiding in Plain Sight

By Minimal Sudoku Team•Last updated: January 28, 2025

Hidden Triples and Hidden Quads extend Hidden Pairs to larger groups. When 3 (or 4) candidates can only appear in exactly 3 (or 4) cells within a unit, those cells must contain only those candidates.

Quick Summary

Hidden Triple: 3 candidates appear in only 3 cells within a unit
Hidden Quad: 4 candidates appear in only 4 cells within a unit
Result: Eliminate all OTHER candidates from those cells
Why "hidden": The cells have extra candidates that obscure the pattern

The Concept

The Hidden Sets rule mirrors Naked Sets: N candidates in only N cells = those cells must contain only those candidates.

Pattern	Candidates	Cells
Hidden Pair	2 candidates	in only 2 cells
Hidden Triple	3 candidates	in only 3 cells
Hidden Quad	4 candidates	in only 4 cells

Not All Candidates in All Cells

A Hidden Triple doesn't require each cell to contain all 3 candidates. As long as the 3 candidates only appear in those 3 cells (and each cell has at least one), it's valid.

The Golden Rule

🔍 Hidden Set Rule

When N candidates appear only in N specific cells within a unit, those N cells must contain those N candidates. Eliminate all other candidates from those cells.

Hidden Triples

A Hidden Triple occurs when 3 candidates can only appear in exactly 3 cells within a unit. The cells likely have other candidates too — that's why the triple is "hidden."

Hidden Triple example in Row 5:

Candidates 2, 4, 7 only appear in cells C2, C5, C8:

Row 5: │ . │[2,4,6,9]│ . │ . │[2,7,8]│ . │ . │[4,7,9]│ . │
            ↑              ↑              ↑
         Has 2,4       Has 2,7        Has 4,7
         
The 2, 4, and 7 ONLY exist in these 3 cells!
→ Remove 6, 9, 8, 9 (the others) from these cells.
→ Result: [2,4], [2,7], [4,7] — now a Naked Triple!

Hidden Quads

Hidden Quads follow the same logic with 4 candidates and 4 cells. They're rare and difficult to spot, but the cleanup is significant.

Very Rare

Hidden Quads are among the rarest patterns in Sudoku. Don't spend too long hunting for them — other techniques are usually more productive.

How to Find Hidden Triples & Quads

Pick a unit

Choose a row, column, or box to analyze.

Map candidate positions

For each missing digit, note which cells can contain it.

Look for limited candidates

Find candidates that appear in only 2-4 cells. These are your building blocks.

Find matching groups

Look for 3 candidates that all appear in the same 3 cells (or 4 in 4 cells).

Eliminate other candidates

Remove all other candidates from those cells — they must contain the hidden set.

Hidden vs Naked Sets

Hidden and Naked sets are mirrors of each other:

👥 Naked Set

N cells have only N candidates

→ Eliminate from other cells

🔍 Hidden Set

N candidates in only N cells

→ Eliminate from those cells

They're Equivalent!

Finding a Hidden Set and eliminating other candidates converts it to a Naked Set. They're two views of the same constraint.

Detection Tips

Count Cell Appearances

For each missing digit, count how many cells contain it. Digits appearing in only 2-4 cells are your candidates for Hidden Sets.

Process of Elimination

In a unit with 9 cells, if you find a Naked Set of 5, the remaining 4 cells form a Hidden Set of 4 (and vice versa). Finding one often reveals the other!

Rarity Guide

Hidden Pairs are common, Hidden Triples are occasional, Hidden Quads are rare. Spend your time accordingly.