Sudoku - sharing skills

[2020hindsight]

lol - embarrassment prevents me from saying how long I took on that evil problem . cheers

 

[Dowdy]

I not bad at sudoku. I was able to do a medium in 10min from the site you gave without any help

 

[2020hindsight]

well done dowdy lol
noone is sharing any skills I notice - but no probs

Here's one of those logic puzzles.
Firstly the clues- and the initial naughts and crosses implied therein :-

 

[2020hindsight]

next the addition of another naught (dead easy - process of elimination) ;

And after that the second naught (based on the large truncated rectangle thingo)

(or if you prefer, truck at zebra = Monday,
and truck at zebra = 10.15am
therefore Monday = 10.15am)

 

[2020hindsight]

then some crosses in the same way , (the two blue ones at least)
(the green crosses are dead easy of course)

you can add the blue crosses based on inequalities or whatever
if Monday equals 10.15am
and Monday doesn't equal Osbourne
then Osbourne doesn't equal 10.15am etc

and so on till the whole thing falls out. (maybe re-reading the clues when you get bogged down)

 

[lesm]

2002,

If you have the time.

A simple example, find the value in the cell containing the '?' and show the steps used.

Cheers.

 

[2020hindsight]

les
ahh pretty easy that one
central 2
then 9th row
then 4th column.
E&OE of course.

When I think about it , you could go straight to 4th column I guess.

 

[lesm]

2020,

Hehe...it was, but I wanted to see how you approached it and show you an alternative approach. Apologies if you are already aware of it.

Not sure of what you are actually aware of, but if you see particular sequences in rows or columns, then you can find the value in a particular cell.

Really helps with the harder puzzles. There are pair and triple combinations that can assist in solving the puzzles faster.

If you have three cells (in a row or column) which contain the same pairs, but one cell has an additional value, then the value of that cell (with the additional value) can be determined.

See below.

 

[2020hindsight]

2020,

1. Not sure of what you are actually aware of, ...

2. If you have three cells (in a row or column) which contain the same pairs, but one cell has an additional value, then the value of that cell (with the additional value) can be determined.

1. yep - first thing a new teacher has to establish lol.
And as you say - a simple example in this case - but the principles, when extended, will assist for the evil ones (I'm hoping lol)

2. btw, I recently became aware of that (as you say - when you get to the harder ones - and hence I started usuing 3 numbers for instance), but I have only rarely used it to be honest . Thanks - will keep it in mind

Furthermore - if you have two cells with (2,or 8), - in one row, or one column , or one 3x3 square - then you know one is 2, and the other is 8. So that only leaves a missing 1 in that column. - almost exactly as you have, but without the need to use 3 options.

PS (but I hear you , I think - sometimes you need to go to three I'm sure)

 

[2020hindsight]

Incidentally, for these easy ones, I'd do as many rows and columns as possible - then , when there are only a few missing in a RCS (row column or 3x3 square), then I'd say eg - "well missing in this row are a 4 and a 7, and by inspection, they must go here and here etc"

 

[lesm]

Correct. The 4 & 7 fall into place and the 8 & 1 in the row below fall into place by elimination.

Another example of the use of pairs, used a hard puzzle this time.

If two cells can only contain 1 of 2 values then any cell in the same row or column cannot contain those values.

Refer to the example below (for illustrative purposes only):

Rows 1 & 2, Column 4 contain the values 1 & 9 and can only contain those values. Therefore, any other cell containing a 1 or 9 in that column can have that value safely removed, as in rows 5 & 6 in the example, where the 1's can be removed.

Where this occurs within a 3x3 square no other cell within that square can contain these values either.

 

[2020hindsight]

thanks les
I'll (hopefully) try out your method on an 'evil' in the next week or so
cheers 2020

 

[lesm]

2020...No probs.

I vary the approach depending on how each puzzle is presented, especially since there are different levels of complexity within a given level.

Either working on rows and colums or the 3x3 squares or a combination of both.

Another approach is to start by working through the numbers from 1 through 9 and find all the obvious ones in each of the 3x3 squares.

Part of it is reducing a higher level down to the next lower level.

Let us know how you go and if using pairs assists.

You run the risk of peeving the Quantas passengers that come behind you, when you start completing them inflight and they don't have a puzzle to finish off.

Cheers.

 

[2020hindsight]

You run the risk of peeving the Quantas passengers that come behind you, when you start completing them inflight and they don't have a puzzle to finish off.

specially if you f*** it up.

 

[RUSHIAT]

Hi, hindsight. I usually do the "evil" sudokus, but I have a different technique to yours. I've attached an image of my first pass of Hard #101 270 313. As you can see I've "pencilled" in all possibilities in each square. The 7,2,1 in the center are self explanatory,(shot 1) which means cell 4,2 must be a 5. Cells 5,1 5,2 5,3 together have to have 3,6 and 7 in them (order unclear at present), which means cells 5,7 5,8 and 5,9 have to have 1,5 and 8 in them (order unclear at present)(shot 2). Cells 6,8 and 6,9 have to share 4 and 7, therefore cell 6,3 must be 2; cell 4,7 must be 6; cell 4,1 must be 4. Cells 1,6 2,6 and 3,6 share numbers 6,7 and 9 (order unclear at present), so cells 7,7 and 7,9 have to share 5 and 8 (order is obvious) and 2,5 has to be 3. Cells 1,5 and 8,5 share 1 and 4, so 9,5 has to be 7(shot 3). In the bottom left square(set of 9 cells) 7,3 8,3 and 9,3 are the only cells with 5 and 8 in them, therefore cells 1,3 2,3 and 3,3 will not have 5 or 8 in them; that leaves 8,3 with 5; 7,1 and 7,3 share 2 and 3, so 9,2 =9 and 9,3 =8, and discard 2 & 3 from the rest of row 7, which leaves 8,4 =3 and 9,9 =3 and 9,8 =2.(shot 4) From there it's a walk in the park.

 

[2020hindsight]

Hi, hindsight. I usually do the "evil" sudokus, but I have a different technique to yours. I've attached an image of my first pass of Hard #101 270 313. As you can see I've "pencilled" in all possibilities in each square. The 7,2,1 in the center are self explanatory,(shot 1) which means cell 4,2 must be a 5. Cells 5,1 5,2 5,3 together have to have 3,6 and 7 in them (order unclear at present), which means .... etc

From there it's a walk in the park.

thanks rush
one thing's for sure - you're more efficient with space lol.
I take about 6 or 7 posts (#18-24) to give details of my "method" - you take one lol. (same puzzle)
cheers , thanks

PS you're very similar to les I believe.

Incidentally, you'd literally need a pencil surely (and an eraser) - so many "workings" during the drafts.

 

[2020hindsight]

I'll throw this one in ..
Sorry haven' t triple checked it ..
I was trying to do it this afternoon before being distracted by family stuff ...
But at that point in time I believed I was stumped ...

btw, the " * " means "7 or 9"
for discussion
cheers 2020

 

[lesm]

Here is the puzzle a number of moves further in. See if you can work out how to get there and we can discuss in a follow up post.

 

[lesm]

The same puzzle after another set of moves.

 

[lesm]

The completed puzzle