|In the above example you can also see that once the 9 is placed, the 7,9 solution in the other cell also became a naked single. This is called a hidden single. So named because they are less obvious until another cell is filled, revealing the useable number in the cell. By penciling all of a cell’s possible number solutions, you can find the hidden solutions much easier.
Hidden Singles :
Hidden singles also only have one position they can fill. The added numbers in the cell hide the solution. When there are lots of numbers showing from the surrounding rows, columns and regions a hidden single is hard to find. Hidden singles are common in Sudoku puzzles.
Naked Pairs :
The next tip for solving Sudoku puzzles is to look for the naked pairs. Naked pairs are two identical number combinations in a certain row, column or region. When you find a naked pair, you can eliminate these numbers from all other possible cells for that row, column or region. This combination is also common in puzzles. Here is a naked pair.
|Hidden Pairs :
Hidden pairs are, like naked pairs, two numbers that can only work in two cells of a column, row or region. The other numbers in these two cells makes the pair hidden and can be hard to spot. While not as common as naked pairs or singles, hidden pairs do occur often.
Naked Triples :
Another tip in solving Sudoku puzzles is to find the naked triples. Like the name states, these are three numbers which have no other numbers in the same cell. But, unlike naked singles or pairs, a naked triple will not always have all three numbers placed in every cell. Sometimes only two numbers are shown, with the third number being set up by the process of elimination. This is a naked triple.
|Hidden Triples :
A hidden triple is harder to spot. The tip about this Sudoku strategy is to look for these in harder puzzles. Hidden triples, like the pairs, have added numbers in the cell which hide the candidates. Hidden triples follow the same rules as a naked triple.
Naked Quads :
Quads are not as common as the other number combinations. Naked quads are like the other types, where the four numbers are restricted to four cells in a column, row or region. Here is a naked quad.