Sudoku Mastery: X Wings, Y Wings & XY Chains

[@christ9359]

Very elegant solution. No crowding up the board early with pointless notes (which is what I tend to do), just seeing the patterns and making the necessary inferences. Nicely done!

[@rabidsamfan]

I enjoyed that one. Your "bent triple" description really helps me understand Y-wings.

[@sheennina1234]

Watching your vids is very therapeutic 👍🏻

[@berylviarisdelesegno4915]

Chain : 9:20 Y-wing : 12:51

[@bachgammon1]

"I want to show that it is possible to solve very hard puzzles without spending three hours looking at every single possibility".. It sounds like you're describing my attempts at level 7 difficulty and upwards killer sudoku puzzles. Do keep your dailykillersudoku live solves coming!

[@CrackingTheCryptic]

I did record a solve of a pretty hard puzzle last week. Your kind words have persuaded me to post it :)

[@bachgammon1]

Cracking The Cryptic Excellent! Killers have been an untalked-of obsession of mine since 2005 albeit with rather less concentration and application than Mark and you can muster. Your solves are absolutely fascinating to me.

[@stefanie5538]

Thanks for these great tutorials! How do you know which one is the pivot cell in the y wing?

[@bluerizlagirl]

The pivot cell is the one that sees one cell in the same box as itself and another cell outside (in the row or column). There must be at least one more cell which is not actually part of the Y-wing but still sees both those other cells. In this grid, A4 can be 4 or 5. B6 can be 5 or 7. A8 can be 4 or 7. Both B6 and A8 see A4. B7, which also sees B6 and A8, can be 2, 5 or 7. If A4 is 4, A8 must be 7. Alternatively if A4 is 5, B6 must be 7. Either way, B7 will see a seven (either in the box, at A8, or in the column, at B6); so the upshot is, B7 actually can never contain a 7; so the 7 in row 7 is forced into column F. It's one of those things that is a lot harder to explain in full than to see in practice. The important thing to notice is, there are two parallel chains of length 3 from A4 to B7, either via A8 or B6; and if _either_ A8 or B6 _must_ contain some digit, then _neither_ A4 nor B7 can contain that digit. (Note that there are other chains from A4 to B7, such as A4-A9-B7 or A4-B4-B7; but these squares are not part of the 4-5-7 triple.)

[@stefanie5538]

@@bluerizlagirl thanks so much! I'll go back through the examples.

[@sanferrera]

@@bluerizlagirl I want to thank you, too. It helped me a lot.

[@ryanoconnor7957]

I don't understand why it's an x-wing on the 8's @4:30 - couldn't r6c2 just contain an 8 as well at that stage? So that means an 8 isn't forced to be in row 5 or 7 of column 2?

[@goldenera7090]

brilliant solve. very useful video again... clearly we have seen Simon's skill on sudoku. now there is a guitar in background in all these videos. perhaps a humble request to see Simon's skills on guitar?? :)

[@CrackingTheCryptic]

I will reveal that hidden away on KZbin it is possible to find 3 (bad) examples of me playing the guitar... To give you the smallest chance of finding the videos, I'll tell you that one of the vidoes is my attempts at Hanuman by Rodrigo y Gabriela :)

[@goldenera7090]

haha I haven't found it yet.

[@glennmelven3414]

@@goldenera7090 Do a YT search for "simon anthony Hanuman". 4th result.

[@shreyaskulkarni5284]

can any1 plz help me to understand how did he put 8 in 5r2c at 9:50. 9:42 : this cant be 4 ? whats the logic

[@paulvn5315]

Great video! Q: at 1:50, why does '1' go in C1R2, when it could have also gone in R3C2? I must be missing something...

[@andresk1685]

In Row 2, we need to complete the 1-9 so we are missing 1, 3, 5...if you look at column 1. It already has a 3 and 5 so a 1 must go in that column and that row.

[@PLF...]

@@andresk1685 thats column 9. Columns are left to right, rows are top down

[@leojf3828]

How come it is SO MUCH easier when he does the puzzle?

[@shayanmoosavi9139]

Because he's a sudoku CHAMPION that's why.

[@hazen7313]

Fr

[@ExodaCrown]

When you did the y-wing, I got the pivot square wrong, but still ended up eliminating 7.

[@hamzahussain7794]

In Y wing explanation, what I dont understand is the pivot square. Why is the r4c1 the pivot square? Does the outcome change if I choose another one of the y wing candidates?

[@MyReligionIs2DoGood]

2 of the 3 squares of the Y-Wing have to be in the same box, and 2 of the squares have to be either in the same row or column. The square that is in BOTH the box AND the row (or column, respectively) is the pivot square. (I know it's late - just answering for the people who might read it later on)

[@jrbr549]

@ 9:41 you made r5c8 an 8. I see how you proceeded down C8 and omitted the 4 in R5C2. But we knew that there was a 48 pair in R5C28. Saying 8 would have made me go farther to the left and put the 4 in to fill out the pair. How did you know to proceed down in column 8? Was it just luck?

[@jrbr549]

My guess since this is a chain video you just followed it through. With my way it would have revealed two 8s in column 8 but more steps to reveal.

[@dvoorganisation459]

Thank you Sir

[@luispalou217]

Best wishes from Mallorca

[@eddiebrookes540]

Hi when you put the 1 in row 2 column 9 how did you know it would not go into row 2 column 3? thanks Eddie

[@sarveshravichandraniyer9661]

There's nothing preventing a 1 in row 2 column 3, but nothing else can come in row 2 column 9 because of 967482 on row 2 and 35 on column 9. So the 1 goes there.

[@jerhurricane]

Do you solve puzzles by request? How do you go about doing that if so?

[@julieannmyers8714]

Send the puzzle via Twitter account.

[@DennisLam]

I'm curious which Sudoku software or app you used in this recording. It looks very user friendly.

[@bukton10]

It's Duncan's SuDoku Solver

[@jeffbrunton3291]

Excellent

[@julieannmyers8714]

5 couldn't be in r4, c3 when you already had 5 in box 1, c3. Minor point, but errors in pencil marking can be confusing at the very least. Impediments to seeing patterns at the worst. Thank you for that 7 elimination with the bent triple. I was stuck but for that one move. You have an uncanny knack for zeroing in on just the right cells! I'm always amazed at that.

[@stefstefstef6789]

Why must the 8s be in row 7 and not row 9?

[@R64GreatDays]

Because the 8s on row 7 are the only places were an 8 can be on. If they are on row 9, you cannot place an 8 on row 7.

[@PeterBrodie]

HELP!!! Last Sunday's Observer killer has got the better of me!🙏🙏🙏

[@CrackingTheCryptic]

I've just taken a look at it. Will post a video in the next day or so :)

[@raphaelzuzak9118]

Nice

[@jokelanddotcom]

No idea how you quickly discount row 9 not also having 8s at C2 and c8 - wouldn’t the same assumed x-wing logic apply there as well?

[@IamMattFleetwood]

Due to the 79 pair in R5, and the 8 in C4-C6 already blocking 8s in that house for R7, we know for certain that the X-wing formation applies to rows 5&7 since C2 and C8 are the only two options/columns for 8s in those two rows. However, the 8s are not limited to only two columns in R9. I hope this helps!

[@erickguz]

@Julia where are you? haha l

[@BozoTheBear]

"Hi"!

[@ResolviendoSudoku]

Great. Atte. Neil Stuar

[@rodkobzey6520]

When it comes to the hard parts like x & y wings you do NOT explain the logic for what you do very clearly. You move thru it too fast. Please slow down when explaining the hard thought out things. Thanks

[@zzzsydneyhom1379]

Too fast for my slow old brain I'm afraid....