Anyone any good at sudoku?

[BlingaRinga]

I need someone to explain this to me! Trying to do a sudoku on the NYT puzzle app and got totally stuck. The app will give you a hint as to which square to try to solve next, and you can also reveal the answer for the square.

The highlighted yellow square is the one suggested that i should have been able to solve, and 9 is the correct answer. However I cannot for the life of me figure out how I was supposed to figure this out - can someone explain!!

Yep, so look at the nine in the top left corner. If you follow that along to the centre it eliminates the whole top line having a nine.

then, look at the nine in the bottom centre square. Follow it up and it eliminates the whole left side having a nine

Sorry, hit post too soon.
it means that in the top centre square there can only be a nine in the right hand column.

follow that down to the centre square and it eliminates the right hand column.
the left hand column is already eliminated from the nine in the bottom centre, and the nine on the left square eliminates the centre line right across - leaving only that one square possible for a 9

I hope that's made sense. I've had two glasses of wine (Saturday night in Australia)

Nope you’ve lost me!

I do sudoku by basically drawing a line across where there already is a 9, which crosses out squares it could potentially go in

In the middle top square, 9 can only go in the bottom right square for the reasons explained by pp.

That tells us that the 9 in the middle square has to be in the middle column. It is therefore in the highlighted square because there is already a 9 in the middle row and the other cell in that column is already filled with a 5.

Hope that makes sense!

So do that starting at the top left square. Cross out the top line in tbe centre square - no 9s can go there

This is much better explained than mine. Sorry!

The way I would look at it is as follows:

The middle vertical column needs a 9 somewhere. It has to be in one of the 5 empty squares. It cannot be in any of the squares in the bottom box because the bottom box already contains a 9. That leaves 2 options in the middle box. One of those options already has a 9 on the horizontal row, so by process of elimination, the yellow square is the only place you can put the 9.

I think the other poster's description should start top center, not top right.

Anyway. Jut look at the column in question. Go cell by cell and identify all cells when a nine can be. I see only one option.

Ah i have got it now! It threw me by suggesting i solve the yellow square next when effectively I had to solve the bottom right square of the top middle box first.

Makes perfect sense to me, but I have had four glasses if wine! In my defence it is 11.00pm in NZ!

Well done!! Also I edited my first reply which basically gave you a bum steer. Sorry.

Haha nice one! 9pm here!!!

Cheers🍷

Actually this is a better explanation for how you can deduce it directly from the existing solved numbers. The other one relies on inferring the position of the 9 in the top middle box.

Look at the vertical lines from left to right.

The first four lines already have a 9, and in the fifth line there are five available spaces (including where the yellow number is).

The bottom three spaces of line five cannot be a 9 as there's already one in that box, and the fifth space from the bottom can't be as there's a 9 on the horizontal line.

That just leaves the square where the yellow 9 is.

The top square vertical is full.

It couldn't be in the bottom square vertical because there's a 9 in the square already.

It therefore has to be in the middle square.

There were two spaces in the middle square vertical and one of those already has a 9 in the horizontal line. So there's only one place it can be.

In general, if you don't see the reasoning behind the hint use pencil marks and check 1) all numbers which are allowed to be on that square 2)for each of those numbers it's possible locations in row, column and 3×3 square.

Surprisingly often if is just a question of noticing that this cell can be filled now.

You're right, this is a much simpler way. Still, I never do them like that!

urgh I am stuck again. Yellow square must be 2 or 7…but which one?!

It's 7.
Can't be 2 because that must go in the middle column of the 3x3 box above it.

Purple lines are crossing out where all the existing 9s rule out squares. Leaving only one place a 9 can go in the top middle set. Red 9. Then the red line rules out more squares as dictiacted by this new 9. Leaving only the highlighted square as an option.

Thinking about both your questions, I think you might benefit from looking at a sudoku the way I was shown. First think of it as divided into three horizontal sections. Look at the top section. Take each number in turn: the number 1 must be in the top row in one of the 3 boxes, the middle row in another box and the bottom row in the third box. Go through each number in turn, doing that, and writing notes in cells if there are only 2 possible cells where that number could be. Repeat for the middle section, then the bottom section.

Then think of the whole thing as three vertical sections and repeat the exercise. Each number must be in the LH column of one box, the middle column of another and the RH column of the third.

The rationale for making notes if there are only two possible cells is that if you have, say, two cells in a box that can both be either 3 or 4, you can rule those numbers out for the other cells. Limiting it to two keeps it manageable. Hope this helps.

Thank you!

Unfortunately somewhere down the line I made a mistake that I couldn’t unpick. An hour of my life wasted! 😭