Demonstration to Sudoku Singles (Hidden Single, Naked Single, Full House)

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 The Singles

Singles may be determined by deleting the numbers already present on the rows, columns, and blocks.

The following strategies provide the solution to most ‘simple’ riddles.

Sudoku Full House Technique

A house (row, column, nonet) is virtually full when only one unresolved cell remains.

It’s quite simple to notice but happens mostly when the grid is virtually solved.

This approach is generally used to produce or grade simple grids and is not helpful elsewhere. The cell is, in fact, both a concealed and naked single.

The last digit

All cells are put in the grid except for one cell for some digit.

Even without pencil lines, it is fairly straightforward to identify.

This approach is generally used to produce or rate simple grids and is not helpful elsewhere.

The cell is, in fact, a secret single for all of its dwellings.

Singles are the most fundamental and simple strategies for solving sudoku problems.

The Full House is the simplest and the greatest, to begin with among them.

The final digit that may be put in a house is a Full House.

A house is a complete collection of numbers ranging from 1 to 9. It might be a row, block, or column.

Here’s an example:

Full House example (1)

Take a look at the home indicated with the blue square; there is only one vacant cell left in this house, marked with a pink square.

After evaluating all of the numbers in the indicated home, we are left with just one unmistakable solution.

Full House example (2)

2 is the only number needed to finish the house.

It is frequently referred to as “Last Digit” if it is the last digit for the whole grid.

Row – Full House

Row - Full House

Here we already have 8 digits occupying the 6th row, which indicates there must be just 1 number left to complete the house, in this instance, a row. So the missing number is two.

Column – Full House

Full House - Column

This time, we’ll have to find the sixth column. We already know 8 of the digits, and a simple check down the column for the ones we already know indicates that the number 4 is our missing digit.

Box – Full House

Full House - Box

We have almost finished a 3×3 box of 9 cells, with 8 of them already filled.

We need only one more number to make it a Full House.

Very immediately, we can tell that 9 goes in the final cell in the home.

Box-filled homes tend to be simpler to identify than rows or columns since we find it easier to concentrate on one location at a time rather than an entire row or column.

In addition, most strategies are simpler to master when they are contained inside a single box rather than scattered throughout the whole grid.

The Final Full House

The last number to be placed into the last empty cell always completes a row, a column, and a box.

The term “hidden single” refers to the fact that only one cell is left to insert that digit for a particular digit and house.

Because more than one candidate remains in the cell, the right digit is concealed among the others.

The Hidden Single is much less evil than its name indicates.

In reality, most Sudoku puzzles published in newspapers and magazines can only be solved using concealed singles simply.

Therefore, it is one of the singles and the Naked Single, the most basic problem-solving approach.

A Hidden Single is a single candidate for a given digit that remains in a row, column, or box.

Additional limitations in Sudoku variations may also result in Hidden Singles.

An alternate word is Pinned digit.

Evaluating 27 houses with each of the 9 numerals, for a total of 243 checks, may seem to be a difficult chore; however, most players do not check each of these combinations separately.

Instead, they use procedures such as Scanning and Cross-Hatching to find the concealed singles.

hidden singles (1)

hidden singles (2)

Consider the following in cell r3c4 of the example just above on it:

According to the rule, the numerals 4, 6, and 9 are all feasible.

However, looking attentively at row 3, we can see that digit 6 can only be inserted in r3c4.

In r2c3, digit 6 blocks r3c1, r3c2, and r3c3, whereas digit 6 blocks r3c6 in r6c6. That is, 6 may be inserted in r3c4.

One of multiple Hidden Singles may be identified in r6c4 in the right example: In row 6, column 4, and block 5, the lone 3 digits 3.

Naked Single’s

The Naked Single is classified as a problem-solving approach, yet it’s hard to call it that.

A naked single is what remains after you have eliminated all other candidates using your problem-solving skills.

In a cell, the final candidate standing is a naked single. Other phrases for this include Forced Digit and Sole Candidate.

The best approach to discover naked singles on the grid is using pencil marks.

Cells with single pencil marks are simple to detect.

Without pencil marks, you need to check the peers of the cell and determine whether there is just a single digit missing in the peers.

It would help if you had a solid short-term memory to perform it this way, although many players answer basic Sudokus without pencil marks.

Most players do not tell other players about their findings of singles. When a Sudoku can be solved with just singles, the problem as a whole is not worth debating.


The digit 8 in the following Sudoku has two Naked Singles.

Naked Single Example

How to Locate Them

Finding Full Houses is simple explanatory.

Unfortunately, hidden and Naked Singles are not so simple to detect.

Nevertheless, they are an excellent illustration of why assigning a difficulty rating to techniques is so difficult: When playing with pencil and paper, Hidden Singles are simple to uncover, but viewing Naked Singles might take some time.

When playing using computer software such as HoDoKu that automatically keeps track of remaining available candidates, finding Naked Singles is straightforward, but locating Hidden Singles may be quite a headache due to the large number of candidates left in the grid (especially early on in the game).

Hidden Singles may be detected by “cross-hatching” while playing by hand: Concentrate on one number and one block at a time.

Then, draw a line across all rows and columns that already have that digit set (in your mind only, please).

If there is just one cell remaining, it is a Hidden Single for that digit.

The figure on the left depicts that procedure for digit 3 in block 5: All cells in that block are “blocked” by putting digit 3, and r6c4 is the last potential cell for digit 3 in block 5.

Another option is to use filters, as seen in the picture on the right.

It is simple to find Singles and Locked Candidate movements when filters are enabled.

Finding Naked Singles by Hand entails filling out all available possibilities or experimenting with promising cells (counting all digits in the cells seeing your intended target cell; if only one possibility remains, it is a Naked Single)How to locate hidden or naked singles

How to find hidden or naked singles

Hidden Singles in Box

Hidden Singles in Line

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