Givens and Candidates
The difference between givens (the fixed starting clues) and candidates (the digits still possible in an empty cell).
Two terms underpin every solve. The "givens" are the digits printed in the puzzle at the start — the clues you are handed. They are fixed and correct, and a good puzzle gives you exactly enough of them to force a single solution.
A "candidate" is a digit that could still legally go in a particular empty cell — one that does not yet appear in that cell's row, column or box. Solving is the process of narrowing each cell's candidates down to one.
Givens: the starting clues
The number of givens is one rough signal of difficulty: fewer clues usually means a harder puzzle. But the placement of the clues matters just as much as the count — a thoughtfully placed clue set can make a sparse grid gentle, while a careless one can make a full-looking grid hard.
Candidates: what is still possible
For any empty cell, list the digits not already used in its row, column and box — those are its candidates. A cell with a single candidate is solved (a naked single). Tracking candidates, by hand or in your head, is how you find the next move.
- A candidate is a digit still legal in a cell.
- Each placement removes that digit from the cell's peers, shrinking their candidate lists.
- When a cell has one candidate left, it is forced.
Frequently asked questions
- Can I ever change a given?
- No. Givens are fixed clues. If a solve seems to require changing one, an earlier placement of your own was wrong.
- Are fewer givens always harder?
- Usually, but not always. Clue placement affects difficulty as much as clue count, which is why two puzzles with the same number of givens can feel very different.
Related reading
Further reading
- Introduction to Solving (candidates) — HoDoKu
- Glossary of Sudoku — Wikipedia
Practice online
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