Hidden Pairs Sudoku Strategy

How the strategy works

Instead of starting with two matching cells, start with two numbers. If both numbers can only fit in the same two cells inside a box, those cells belong to that pair.

Other candidate marks in those two cells can be removed because the pair must occupy them.

Large print practice routine

Use this technique slowly on a readable board or a printed sheet. The goal is to remove uncertainty, not to solve faster.

After each candidate cleanup, return to scanning and singles before looking for another advanced pattern.

Hidden pairs are a good reason to review candidate notes rather than adding more of them. The move is useful when a row, column, or box has several marks, but two numbers keep appearing in exactly the same two places.

• Pick one row, column, or box.
• Check where each missing number can still go.
• Look for two numbers with the same two possible squares.
• Clean those two squares and search for singles again.

Example pattern

Example: a box is missing 1, 3, 5, and 9. After checking crossing rows and columns, 1 can go only in the top-left or bottom-left empty square, and 5 can also go only in those same two squares.

Those two squares must contain 1 and 5 in some order. Any other candidate notes in those two squares can be removed because the pair is hidden inside the candidate list.

Common mistakes to avoid

Do not confuse hidden pairs with two cells that merely share candidates. The hidden pair starts from two numbers and their only two possible locations.

Do not erase candidates from the whole puzzle. Clean only the two pair cells inside the row, column, or box where the pair was proven.