Beginner Techniques - Hidden Singles in Sudoku

Hidden Singles in Sudoku

There are many websites that purport to find hot singles in your area, we can offer no such thing, however, we can help you find hidden singles in your sudoku puzzles.

What's a Single?

In Sudoku, a single is a cell such that there is only one possible number that can occupy it. A naked single is a cell where the only candidate is obvious.

Here, we can see that the house that the cell is in contains 1, 2, 3, 8, 9. This leaves 4, 5, 6, 7 as its possibilities. But, its row contains 4, 6 and the column contains 7. Thus, the solution must be 5. This is a typical naked single.

What's a Hidden Single?

A hidden single is a cell where there’s only one possible candidate but its less obvious. This can be because even though all the other candidates are not eliminated by numbers in the row/column/house, there is no other cell that one of the candidates can go in.

Here, we can see that this cell has a lot of possibilities: 1, 5, 6, 7, 8, 9 even after we eliminate numbers that are in the row/column/house.

However, notice that 8 cannot go in any other cell of the house. This house must contain an 8 so this is the only possible place it can go. Bingo!

This was an example of a hidden single in a house but the same principle can be applied in a row or column. Sometimes, hidden singles can be uncovered without having having too many notes but some of them can be really hidden.

P.S. The graphics you see in this post are all directly from the hint system of Not Evil Sudoku. When you request a hint it’ll highlight the house/row/column that contains the naked single and highlight the cell where it appears.