"Hidden Pairs"Technique
What is a "Hidden Pair"?
The "Hidden Pairs" technique is the next level up from "Hidden Singles". It requires players to scan the notes of an entire block, row, or column to find a special pair.
"Hidden" vs. "Obvious" Pairs
An "Obvious Pair" is when two cells have only the same two notes (e.g., {7, 9} and {7, 9}).
A "Hidden Pair" is when two numbers (e.g., '2' and '6') appear as candidates only in two specific cells within a house, but those cells also contain other notes (e.g., {2, 3, 4, 6, 8} and {2, 4, 6, 7}).
The Logic Behind It
If the numbers '2' and '6' only appear in Cell A and Cell B within this block, then Cell A and Cell B must be 2 and 6. Therefore, we can confidently eliminate all other notes from those two cells.
How to Find a Hidden Pair
Let's look at the example in the middle-right 3x3 block.
In this block, we can see the following filled numbers and notes:
- Filled Numbers: 5 (R4C8), 1 (R6C8).
- Notes (Candidates):
R4C7 = {4, 8, 9}
R4C9 = {2, 3, 4, 6, 8, 9}
R5C7 = {3, 4, 7, 8}
R5C8 = {3, 4, 7, 8}
R5C9 = {2, 3, 4, 6, 7, 8}
R6C7 = {3, 4, 7, 8}
R6C9 = {3, 4, 7, 8, 9}
Step 1: Scan the Block for a Pair
We must scan the notes of all 7 empty cells, looking for two numbers that appear only twice.
Scan for '2': The note '2' only appears in cells R4C9 and R5C9.
Scan for '3': Appears in 5 cells.
Scan for '4': Appears in 6 cells.
Scan for '6': The note '6' only appears in cells R4C9 and R5C9.
Scan for '7': Appears in 4 cells.
Scan for '8': Appears in 6 cells.
Scan for '9': Appears in 3 cells.
Step 2: Lock the Pair
We found our "Hidden Pair": {2, 6}. These two numbers only appear in the same two cells (R4C9 and R5C9). This means these two cells must be 2 and 6.
Step 3: Eliminate Other Notes
Now that we know R4C9 and R5C9 must be 2 or 6, we can remove all the other "victim" notes from those two cells.
- For R4C9: The notes were {2, 3, 4, 6, 8, 9}. We eliminate 3, 4, 8, and 9. The notes become {2, 6}.
- For R5C9: The notes were {2, 3, 4, 6, 7, 8}. We eliminate 3, 4, 7, and 8. The notes become {2, 6}.
By finding this "Hidden Pair", we have successfully cleaned up our notes and created a new "Obvious Pair"!
Master This Scanning Technique
This technique is a major step in solving harder puzzles. It trains your eyes to scan for patterns, not just individual cells.
Ready to Practice the “Hidden Pairs” Technique?
Reading about Hidden Pairs is helpful — spotting them in a real puzzle is where the skill really sticks.
👉 Play Classic Sudoku Online
Start with a Medium puzzle, turn on Notes, and scan each block to find pairs of numbers that appear only twice.
Tip: If you can identify one Hidden Pair without guessing, you’re officially moving beyond beginner level.