An example Descriptive Pairs puzzle. Beside row 1 the pair {1, 5} holds because the 1st cell is 5 - the 5th cell being a 1 would satisfy it too.
Descriptive Pairs Sudoku writes a pair of digits outside some rows and columns. The pair describes a position relationship, and it is deliberately ambiguous: for the clue {X, Y}, either the Xth cell holds Y, or the Yth cell holds X - and possibly both. You never learn which from the clue alone; the rest of the grid settles it. It is a cousin of Numbered Rooms, loosened into an "at least one" rule.
The rule: at least one of the two holds
Take the clue "3 7" beside a row. Counting inward from that edge, either the 3rd cell contains a 7, or the 7th cell contains a 3 - at minimum one is true. Below, the 3rd cell resolves to 7 (the 7th cell could still be a 3 as well).
Clue {3, 7}: here the 3rd cell holds 7 (green). The other option - the 7th cell (blue) holding 3 - may also be true, but at least one must be.
How to read it
The clue is a disjunction. It rules out only the case where neither relationship holds. Early on that is weak, but it grows sharp as the grid fills: the moment you know the 3rd cell is not 7, the clue forces the 7th cell to be 3, and vice versa.
Equal-looking pairs are special. A clue like {2, 2} is really just "the 2nd cell is 2", since both halves say the same thing - an exact placement.
Solving strategy
- Wait for one side to fail. As soon as one of the two positions is blocked, the other becomes a forced placement.
- Use the digits as exclusions. Whichever way it resolves, both X and Y are constrained to specific early cells, keeping them out of others.
- Prize the tight positions. Small numbers in the pair point at cells near the edge, where the near box also limits the options.
- Feed the grid. Every digit a pair fixes behaves like a given for its row, column and box.
Common mistakes
- Assuming both hold. Only at least one is guaranteed - do not place both until the grid proves it.
- Fixing which side is true too early. The clue is symmetric; let other constraints break the tie.
- Counting from the wrong end. Always count inward from the edge the clue is written on.
- Dropping ordinary Sudoku. The placed digits must still obey their row, column and box.
Can I play it here?
Not yet - Descriptive Pairs Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile:
- Browse all the Sudoku variants we do offer.
- Or print free puzzles from the printable PDF page.
Where to play it
Descriptive Pairs Sudoku belongs to the constraint family and runs on 9×9. It is not one SudokuStreak generates yet - but the deduction it trains is the deduction every Sudoku runs on.
Difficulty and type are two separate dials here: the type sets the extra rule, the level sets how much of the grid you start with. Expert Sudoku leaves 25 of the 81 cells filled, where the beginner tools dry up almost entirely; Evil Sudoku leaves 23, with no easy moves at all. Take it at the gentler end while the pattern is still new, and move up once it stops being a fight.