Sudoku Naked Single
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You'd like to translate the site? Singles can be identified by eliminating the s already present on the rows, columns and blocks. The following methods permit the solution of most 'easy' puzzles. A can be ased to a cell when it is the only possibility, given the row, the column and the block that contain the cell in question.


Naked singles appear in every sudoku puzzle you solve and is where a cell has only one possible option left. Eight of the s from 1 - 9 already appear elsewhere in a house that cell belongs to, or all other candidates have been eliminated from that cell through more advanced techniques such as pointing and claiming. Spotting naked singles when using candidates is very simple If you are playing without using candidates though, which is typical for easy puzzles especially with pencil and paperthen you will tend to locate all the single singles first and only look for naked singles when you have exhausted all the hidden singles, as they are more difficult to spot.

There is no single solution path that you have to take and whether you focus on hidden or naked singles will be determined by your preference and use of candidates. Sometimes, the same puzzle like this one can be solved by using entirely hidden singles, or by using entirely naked singles! However, there will be times when you will be forced to find Sudoku hidden or naked single to make progress.

Naked Single in Row 5 Col 8 The difficulty with finding naked singles, without candidates, is in forming a memory map of which s naked occur in one of the three houses row, column, box. You can't simply scan one house, or use a cross-hatching method to reveal them like you can with hidden singles.

Essentially you have to check each cell and remember how many distinct s that cell can "see", and what options are still possible for that cell and if it's only one, it's a naked single!

By picking a cell and working methodically through the s from 1 Sudoku 9, you can count the of options still available as you go. As soon as you find two s that could possibly be in that cell or in other words, two s the cell can't "see" in any of the three connected houses you know it isn't a naked single and can stop checking that cell. Choosing which cells to check is difficult, but you know that the total of digits in each of the cell's three houses must be at least 8 to have a chance of seeing the 8 distinct s required.

You can expect s to be repeated across the three different houses but not within of course and you only need to eliminate each once, but there is no point testing a cell for a naked single where there are only 3 digits in the same row, 2 digits in the column and 2 digits in the same box for example, as that is only 7 possible s that can be eliminated from 9, so there must be at least 2 possibilities single. If a digit is in the same row or column but also in the same box then it only counts once as it is part of two overlapping houses to that cell.

By looking for cells with digit counts of eight or higher in the three houses combined you are more likely to find a naked single. In this example you can see that the cell r1c2 row 1 column 2 has the s 1, 3, 4, 5, 6, 7, 8 and 9 in at least one of the three houses it is part of and means that this cell can only be the 2 as it is the only is cannot "see".

Naked pairs

There are 9 intersecting digits in total. The s 6, 3, 9, 8, 5 appear in the same row. The s 1, 7 appear in the same column. And the s 6, 3, 1, 9, 7, 4 appear in the same box.

The 9 is found twice, once in the row and once in the box, while the s 1 and 7 are in both the cell's box and column. Naked Single in Row 3 Col 7 The r3c7 cell can "see" 12 digits, 8 of which are distinct.

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The only it can't "see" in any of the three houses is 3, so that must be the only than can go in that cell! The 9 appears single in the cell's row, column and box, for a total of 3 times. The Sudoku 5 and 7 appear twice each - in a box and column, and a row and column relationship. Each naked appears once in either the row, column or box the cell is part of. The of times a cell can "see" a particular is not important, other than to realise any one of these eliminates it from being a candidate for that cell. The important thing is to establish that it can see 8 distinct s leaving only one option for that cell.

When you add the candidates to the puzzle you can see immediately where the naked singles are! You may find that you want to use candidates, or want to fill in all the "easy" singles first before resorting to using candidates to save time by not having to write so many in.

Hidden singles

All techniques, other than full house, hidden single and naked single, don't actually tell you what goes in a cell, only what doesn't go in a cell! This is known as a process of elimination and in doing so you reduce the puzzle down to hidden and naked singles. But when you can't solve a puzzle using just these two techniques and get stuck, this is the point where you will want to start thinking about using candidates to keep track of any eliminations!

Hidden Singles. Play online sudoku now or check out our Sudoku Puzzles: Easy to Extreme book!

Naked singles

Or start off with Easy Sudoku Puzzles. What gas mark is equivalent to o F? Finding Naked Singles is simple using candidates! Naked Single in Row 1 Col 2 In this example you can see that the cell r1c2 row 1 column 2 has the s 1, 3, 4, 5, 6, 7, 8 and 9 in at least one of the three houses it is part of and means that this cell can only be the 2 as it is the only is cannot "see".

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The definition of a hidden single is when a pencil mark is the only one of its kind in an entire row, column, or block.


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Singles are the most basic techniques in solving sudokus and within the singles the Full House is the easiest as well.