sudokUI › Sudoku techniques › Hidden Pair
Hidden Pair in sudoku
flip side of a naked subset · in a line: X-Wing sideways · how it fits
Two digits X and Y, both still missing from a unit, whose only places in that unit are the same two cells.
Why it works
The unit needs both X and Y, and only these two cells can take them, so one cell must be X and the other Y. Remove all candidates except X and Y from both cells.
How to spot it
Go through a unit digit by digit, noting where each can go, and watch for two digits limited to the same two cells.
Worked example
Hidden Pair: in row 4, digits 6/8 fit only in r4c3, r4c7, so all other candidates there can be removed.
Practise it on a real puzzle. sudokUI generates a puzzle that needs Hidden Pair and takes you straight to the position where it applies. Hints draw the pattern on the board and explain the step.
In a puzzle's rating
Each time the solver needs Hidden Pair, the puzzle's difficulty rating grows by 70. Its class is Medium. It is needed in 1 in 24 puzzles that sudokUI generates. How the rating works.
More subsets
Naked Pair · Naked Triple · Hidden Triple · Naked Quadruple · Hidden Quadruple