dailysudoku.com

[Marty R.]

There it was, we're back in business. But I couldn't find a February 1 or 2.

[nataraj]

back in business, and a good solid vh.


Not quite easy to spot x-wing (5) and then xy-wing 46-24-26 did it.
Looking forward to seeing other solutions.

[Marty R.]

[tlanglet]

After the basics, I found a finned x-wing to delete a <5> at r8c5, but I am not sure that really helped because coloring on <6> resulted in six deletions that broke the puzzle open.

Ted

[Mindwarp]

Ah we are back, unfortunately for me it is one of those VH's for which will have to go in the unsolved archive. I just don't have the techniques for solving this variety. All I do is stare at it for ages not able to see any way through.

[Johan]

When the grid is loaded with multivalue cells after basics, first thing I search for are some ER's, being a P&P solver I find these ER's easier to find than

an x-wing, but that's just from one's own experience, because they sometimes overlap x-wings and finned x-wings, others may find x-wings easier too spot.

An ER for digit <6> in Box 1 takes out <6> in R5C1, the eri(Empty Rectangle Intersection) in R1C1 can see one of the strong link* on <6> in C6, collapsing

the whole puzzle.

[storm_norm]

x-wing on 5

coloring on 6

SE 4.2

[nataraj]

[melis]

Although I've been doing sudoku for a year or so, I'm a newbie with terms and techniques having only recently discovered sudoku online. A big thank you to for your 'tutorial'. It's not the techniques but finding the patterns that I find challenging and your advice was extremely useful. Now I have a plan....bring on those VH!!

[melis]

OK, got the 5 x-wing and cleaned it up a bit, but am stuck again! Just don't want to give up, otherwise I'm never going to learn. Any advice?

[ravel]

There is one more advanced step needed (i suppose you noticed the pairs and had some singles).

[nataraj]

Again, it is helpful to use a search pattern.

Try this on for size:

Starting at the top left, take one row at a time, going from left to right, and look for bi-value cells (those cells with exactly two candidates in them).

In ravel's grid, the first such cell would be r1c2 {2,4}

For each cell found, look
- to the right in the same row
- down in the same column
- in the same box
and see if there are any other bi-value cells that share one candidate with the first cell found

In ravel's grid, that "second cell" would be r1c6 {2,6}

Now we need to look for the third cell that makes up the xy-wing. And as it happens, we know exactly what to look for: a cell with {4,6} in it that "sees" either the first or the second cell. We don't have to look far:
- row 1,
- columns 2,6
- boxes 1,2

Now, aren't we lucky today? r3c1 is such a cell! And we have found an xy-wing. Remains to see whether it solves anything: this xy-wing (46-24-26) removes 6 from all cells that see r3c1 and r1c6, and that would be r1c3 and r3c5. r3c5 is especially valuable, because it solves a cell r3c5=2.

Usually, at this point the search stops and we solve the sudoku.

Just for demonstration purposes, let us continue the search pattern.

There are no more cells with {4,6}

Look for other "second cells":
- nothing in row 1
- {4,5} in col 2 (r4c2). Look for {2,5}. No such luck
- {4,6} in box 1 r3c1. Look for {2,6) ... r1c5, we got that. r3c5 is good!

We found another xy-wing. This xy-wing (24-46-26) removes 2 from all cells that see r1c2 and r3c5, there is only one such cell r1c6 and it solves r1c6=6

No more second cells can be found, continue with all other possible first cells:

Take {2,6} in r1c6. The search becomes progressively faster because we only need to look right and down and box, not left and up (we already did these).

Possible "second cells": only one.
{2,4} (r9c6), with third cell {4,6}: such a cell exists, but not in rows 1,9, col 6 or boxes 2,8 -> no wing

Next "first cell": [3,9} in r2c1.
Second cells: none in r2, {3,4} in c1 (but no third cell {4,9}), none in box 1.

And so on.

A simple search pattern, guaranteed to find xy-wings if any exist.
And fast. The long explanation may look forbidding, but with a little practice it takes only a few minutes for the whole puzzle.

Only a little longer if one includes xyz-wings in the search.

Good hunting! Waidmannsheil!

[George Woods]

Taking Ravel's grid there is a simple W wing - the 24s in boxes 1 and 3 acting on row 2! It then falls out!

The difficulty for me is getting to Ravel's grid!

[Wendy W]

Thank you, Nataraj! I completely overlooked that vertical x-wing on the 5's.
Good VH puzzle for Super Bowl Sunday.