Hidden Pair

Level 3 · Yellow Belt

Strategy:

Requires:

Learn after:

Overview

A Hidden Pair occurs when two candidates appear in exactly two cells within a house, even though those cells may contain other candidates. Since those two digits must go in those two cells, all other candidates can be eliminated from them.

How It Works

Within a house, find two digits that appear as candidates in exactly the same two cells.
These two cells are the only places for those two digits within the house.
Eliminate all other candidates from those two cells, leaving only the pair.

Example

Look for Hidden Pair.

Sudoku grid showing the initial puzzle state for Look for Hidden Pair.

1

Hidden Pair

Check digits 3 and 5 in row 1.

Sudoku grid illustrating step 1: Hidden Pair — Check digits 3 and 5 in row 1.

2

Hidden Pair

r1c4 is already filled with 2.

Sudoku grid illustrating step 2: Hidden Pair — r1c4 is already filled with 2.

3

Hidden Pair

r1c8 is already filled with 7.

Sudoku grid illustrating step 3: Hidden Pair — r1c8 is already filled with 7.

4

Hidden Pair

r1c9 is already filled with 4.

Sudoku grid illustrating step 4: Hidden Pair — r1c9 is already filled with 4.

5

Hidden Pair

Digit 3 cannot go in r1c2 because r4c2 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 5: Hidden Pair — Digit 3 cannot go in r1c2 because r4c2 is already in this column. Remove the entry or choose a different digit.

6

Hidden Pair

Digit 3 cannot go in r1c5 because r5c5 is in this column and r3c4 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 6: Hidden Pair — Digit 3 cannot go in r1c5 because r5c5 is in this column and r3c4 is in this box. Remove the entry or choose a different digit.

7

Hidden Pair

Digit 3 cannot go in r1c6 because r7c6 is in this column and r3c4 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 7: Hidden Pair — Digit 3 cannot go in r1c6 because r7c6 is in this column and r3c4 is in this box. Remove the entry or choose a different digit.

8

Hidden Pair

Digit 3 cannot go in r1c7 because r2c8 is already in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 8: Hidden Pair — Digit 3 cannot go in r1c7 because r2c8 is already in this box. Remove the entry or choose a different digit.

9

Hidden Pair

Digit 5 cannot go in r1c2 because r8c2 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 9: Hidden Pair — Digit 5 cannot go in r1c2 because r8c2 is already in this column. Remove the entry or choose a different digit.

10

Hidden Pair

Digit 5 cannot go in r1c5 because r2c5 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 10: Hidden Pair — Digit 5 cannot go in r1c5 because r2c5 is already in this column. Remove the entry or choose a different digit.

11

Hidden Pair

Digit 5 cannot go in r1c6 because r2c5 is already in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 11: Hidden Pair — Digit 5 cannot go in r1c6 because r2c5 is already in this box. Remove the entry or choose a different digit.

12

Hidden Pair

Digit 5 cannot go in r1c7 because r3c7 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 12: Hidden Pair — Digit 5 cannot go in r1c7 because r3c7 is already in this column. Remove the entry or choose a different digit.

13

Hidden Pair

These two digits appear only in columns 1 and 3, so row 1 has reserved those cells for them.

Sudoku grid illustrating step 13: Hidden Pair — These two digits appear only in columns 1 and 3, so row 1 has reserved those cells for them.

14

Hidden Pair

That means those two cells must end up as 3 and 5 in some order.

Sudoku grid illustrating step 14: Hidden Pair — That means those two cells must end up as 3 and 5 in some order.

15

Hidden Pair

Any other candidates still written in those two cells are extra and must be removed.

Sudoku grid illustrating step 15: Hidden Pair — Any other candidates still written in those two cells are extra and must be removed.

16

Hidden Pair

Remove every candidate except 3 and 5 from those two cells.

Sudoku grid illustrating step 16: Hidden Pair — Remove every candidate except 3 and 5 from those two cells.

17

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

Look for digits that appear rarely (2-3 times) within a house.
After finding a Hidden Pair, check if it creates Naked Singles.
Hidden Pairs are often easier to spot in blocks than in rows/columns.