Hidden Single Practice Puzzles

Every puzzle below is verified to feature the Hidden Single as its hardest required technique — of the 65,284 puzzles in our library, 62,669 require it and 6,589 need nothing harder. New to the pattern? Learn the Hidden Single or see a worked example first.

How to drill the Hidden Single

A Hidden Single is found by asking a different question from the one that finds a Naked Single. Instead of looking at a cell and asking what can go in it, you take a digit and a unit and ask where that digit can still live. If only one cell survives, it is forced, however many other candidates that cell happens to show.

That inversion is the whole point of the drill, and it is why these puzzles reward a fixed search order rather than wandering. Work one digit at a time across all nine boxes before moving to the next digit; the alternative — scanning a box for whatever turns up — makes it far too easy to miss the digit that only just became constrained.

The most common failure on these grids is checking boxes only. Hidden Singles hide in rows and columns exactly as often, and a solver who cross-hatches boxes alone will stall on puzzles that are not actually hard.

Curated Hidden Single puzzles

  1. Practice puzzle #1 — 25 givens · needs Naked Single, Hidden Single
  2. Practice puzzle #2 — 24 givens · needs Naked Single, Hidden Single
  3. Practice puzzle #3 — 24 givens · needs Naked Single, Hidden Single
  4. Practice puzzle #4 — 22 givens · needs Naked Single, Hidden Single
  5. Practice puzzle #5 — 25 givens · needs Naked Single, Hidden Single
  6. Practice puzzle #6 — 25 givens · needs Naked Single, Hidden Single
  7. Practice puzzle #7 — 24 givens · needs Naked Single, Hidden Single
  8. Practice puzzle #8 — 20 givens · needs Naked Single, Hidden Single
  9. Practice puzzle #9 — 25 givens · needs Naked Single, Hidden Single
  10. Practice puzzle #10 — 23 givens · needs Naked Single, Hidden Single
  11. Practice puzzle #11 — 24 givens · needs Naked Single, Hidden Single
  12. Practice puzzle #12 — 24 givens · needs Naked Single, Hidden Single
Get a fresh Hidden Single puzzle →

Hidden Single practice FAQ

How many Sudoku puzzles require the Hidden Single technique?
Of the 65,284 puzzles in the Precision Sudoku library, 62,669 require the Hidden Single to solve, and 6,589 can be completed with nothing harder than the Hidden Single. Every puzzle is verified by a solver that records the exact techniques needed.
Why do I keep missing Hidden Singles that seem obvious afterwards?
Almost always because the cell showed several candidates and your eye skipped it. A Hidden Single is hidden precisely because the cell looks unresolved. Scanning by digit rather than by cell removes the problem: once you are asking where a 7 can go, a cell full of other candidates is still a candidate cell for the 7.
What scan order works best for these puzzles?
Pick a digit, sweep every box for it, then every row and column, then move to the next digit. A fixed order is slower for the first few puzzles and considerably faster after that, because you stop re-checking regions you have already cleared.