How to Solve Sudoku Puzzles with Hidden Pairs, Hidden Triplets, and Hidden Quads
Hidden Pair, as the name suggests, involves finding two cells in a row, column, or 3x3 that have only two possible , and those candidates are the same in both cells. These two candidates are hidden among other candidates in those cells, and may not be immediately obvious. The presence of these hidden pairs means that those two candidates must appear in those two cells and no others, so any other candidates in those cells can be eliminated.
In the image, the yellow cells only contain the candidates 5 and 6 in the 3x3 box that they are a part of. Therefore we can remove the other candidates: 8.
Similarly, Hidden Triplets and Hidden Quads work on the same idea, but instead of looking for pairs of numbers, you look for groups of three or four numbers, respectively. In Hidden Triplets, three cells in a row, column, or 3x3 box share three candidates, while in Hidden Quads, four cells share four candidates.
These techniques may be more challenging to spot than Naked Pairs, Triples, and Quads, but they can also be more powerful in reducing the number of candidates in the puzzle. Knowing these techniques can be helpful in solving Sudoku puzzles of varying difficulty levels.
