The New Sudoku Players' Forum

[Steerpike58]

This may seem like a really dumb or strange question, but I found myself using this technique several times today with one particular puzzle. Bottom line is, it was easier for me to spot a 'naked triple' than it was to spot a hidden single. I eliminated all the items due to the naked triple and that left the 'hidden single' in plain sight. I'm still learning techniques, and today I was really focusing on hidden and naked pairs and triples, so my brain was primed to see the triple more than the single. I just wanted to verify - is this a legitimate, though perhaps odd, approach?

The sample below represents 3 boxes out of 9.

Code: Select all

      1   2   3
  ---------------
A  !  5   2  38  !
B  !  38  6  7   !
C  !  89  4  1   !
  ---------------
D  !  6   9  5   !
E  !  28  1  48  !
F  !  238 7  38  !
  ---------------
G  !  4   5  2   !
H  !  7   38 389 !
J  !  1   3  6   !
   ---------------


In column 1, we have the naked triple B1/E1/F1 (38, 28, 238). This naked triple therefore eliminates the '8' in C1, leaving '9' as the only candidate in C1.

The entire puzzle is:

....9..2.4.25...6..53.7..4..78..1...9...5.....4.6..........7..25...4.7........1.6

I found several examples where I was able to eliminate candidates using naked pairs, naked triples, and possibly more, and yet the online 'solver' showed me that it was entirely solvable using only naked and hidden singles!

[Leren]

Hi Steerpike58,

As a card carrying member of the LMS (that's Lousy Manual Solver) club, I've always thought that Hidden things are harder to spot than Naked things, whilst other's seem to think the opposite is true.

Don't feel too bad about missing the Hidden Single, it won't be the first time that's come up and it won't be the last. See a recent example here. OMG it was you It looks like your DNA and Hidden Singles just don't get on too well.

Leren

[Steerpike58]

Here's a puzzle I found online, which clamed to be 'expert'.

...724...1...9....9.6.3....58.....6......7.3....8..9....23....7.9....4.2..4......

It has 3 naked pairs, and 6 naked triples, and nothing more (no hidden items, and nothing more complicated). Good exercise for anyone looking specifically to practice naked items! I even found a naked quad, but the 'solver' at 'Sudokuwiki.org' only found the pairs and triples, presumably because it eliminated the quad before it got to it.

[Leren]

12..386.......7.8............7.........3.14...4....2956....432...........8..23.46

This one has a naked pair with 18 eliminations. Leren

[eleven]

Steerpike58, if you look at the givens/solved cells instead of the candidates, you will spot the hidden singles, pairs etc much easier than the naked sets - and you don't need to fill the candidates in.
In your puzzle

Code: Select all

 +-------+-------+-------+
 | x x x | 7 2*4*| . . . |
 | 1 . x | . 9 . | . . . |
 | 9 . 6 | . 3 . | . . . |
 +-------+-------+-------+
 | 5 8 . | . . . | . 6 . |
 | . . . | . . 7 | . 3 . |
 | . . . | 8 . . | 9 . . |
 +-------+-------+-------+
 | . . 2*| 3 . . | . . 7 |
 | . 9 . | . . . | 4 . 2 |
 | . . 4*| . . . | . . . |
 +-------+-------+-------+


you have 24 given both in row 1 and column 3. So both cannot be in r1c123 and r2c3. So they must go to r23c2 in box 1 (hidden pair). This leaves only r2c3 for 7, and the rest are singles.

[Steerpike58]

Steerpike58, if you look at the givens/solved cells instead of the candidates, you will spot the hidden singles, pairs etc much easier than the naked sets - and you don't need to fill the candidates in.
In your puzzle

Code: Select all

 +-------+-------+-------+
 | x x x | 7 2*4*| . . . |
 | 1 . x | . 9 . | . . . |
 | 9 . 6 | . 3 . | . . . |
 +-------+-------+-------+
 | 5 8 . | . . . | . 6 . |
 | . . . | . . 7 | . 3 . |
 | . . . | 8 . . | 9 . . |
 +-------+-------+-------+
 | . . 2*| 3 . . | . . 7 |
 | . 9 . | . . . | 4 . 2 |
 | . . 4*| . . . | . . . |
 +-------+-------+-------+


you have 24 given both in row 1 and column 3. So both cannot be in r1c123 and r2c3. So they must go to r23c2 in box 1 (hidden pair). This leaves only r2c3 for 7, and the rest are singles.

More good insight! So in box 1, you can eliminate 2, 5, 7 from B2, and 5, 7 from C2 using the hidden pair 24 (which leads to the hidden single 7 in B3). I don't understand your comment 'and the rest are singles' (but I'm still a newbie!).

I've tried several times to do a 'quick pass' looking for obvious singles, based on 'givens'/'solved cells', but I find myself often spinning my wheels relative to just 'biting the bullet' and 'getting on with it', working out the candidates methodically for each cell. A compromise I'm leaning towards at the moment is to start working out the candidates for the 'most populated box', on the assumption that that box will have the highest likelihood of quick singles being revealed. Another strategy I've tried is looking at which number is most prevalent on the board at the start, and assume that that number is going to be the easiest one to find singles for - but that's probably not valid.

At the moment, being a complete newbie (but now armed and moderately capable with all the 'basic' strategies up to X-wings and Y-wings - struggling to grasp 'basic coloring' at the moment), I feel a bit overwhelmed by the number of possible strategies, and find it quite tedious to go through looking for last candidates over and over, after each 'discovery' (by row, by column, by box). But - I just need to keep practicing! I'm starting to see naked triples leaping out at me now, while a few days ago they were a struggle. So I need to keep plodding on! I also want to avoid easy puzzles that don't require anything but hidden singles, but also avoid puzzles that get into the real nitty gritty stuff (extreme and diabolical strategies). If I'm on my laptop, I just stick to 'Sudoku Solver' (sudokuwiki.org) but sadly, I downloaded his android app and it's totally unusable so I find myself trying random other android apps, and then I discover that every app seems to have its own definition of difficulty. I tried an 'Expert' puzzle at sudoku.com (which has a beautiful, easy-to-read layout) and solved it entirely with naked pairs. So for my phone, I need an app that has easy-to-read graphics, and also a rational difficulty rating!

Anyway - thanks for the insight!

[StrmCkr]

and the rest are singles.

means the remainder of the puzzle is only Naked / Hidden singles and no other advanced techniques need to be used.

[Steerpike58]

Hi Steerpike58,

As a card carrying member of the LMS (that's Lousy Manual Solver) club, I've always thought that Hidden things are harder to spot than Naked things, whilst other's seem to think the opposite is true.
...
Leren

I just found this online sudoku page -
https://sudoku.simonton.app/
It has a nice way of presenting analysis, and allows you to choose which solution is applied.

For example, you can load this fairly basic puzzle into it:

57......24...8.6..2.6....7.....64.5.....91.6......2.4.89......77...4.1..1.2....8.

and on the right side, it shows that, for this instance of the game, there are 2 lone singles, 4 hidden singles, 9 'omissions' (which are pointing pairs and box line reductions), 1 naked pair, 1 naked triple, 1 hidden pair, and more. But if you load it into sudokuwiki.org and analyze it, the entire puzzle can be solved by singles and it never presents anything beyond that since it always takes simplest solution first. I find that my eye/brain latches onto pointing pairs quite nicely, so this is helping to validate what I'm finding!