## Found this Su Doku very difficult, can you help?

Post the puzzle or solving technique that's causing you trouble and someone will help

### Found this Su Doku very difficult, can you help?

Managed to solve only two numbers!

[14][19]6,8[259]3,7[12][245]
52[78],[67]41,[68]93
[1347][1789][134789],[2567][25679][259],[12468][128][24568]

[127]4[178],9[238]6,[238]5[278]
9[678][578],[245][2358][245],[2368][2378]1
[26]3[58],1[258]7,94[268]

[13467][1679][13479],[24567][25679][2459],[12348][12378][2478]
85[347],[247]1[24],[234]69
[1467][1679]2,3[679]8,5[17][47]

Not having much experience with X Wing, I was going to eliminate 4 from c1r3, c1r7,c9r3 & c9r7. Also eliminate 9 from c2r3 c2r7 & c5r3 c5r7
IS that correct? What next?
Kites

Posts: 48
Joined: 20 May 2005

Look in Column 3. Consider which cells the values 1, 3, 4 and 9 could occupy.
Sue De Coq

Posts: 93
Joined: 01 April 2005

[quote="Sue De Coq"]Look in Column 3. Consider which cells the values 1, 3, 4 and 9 could occupy.[/quote]
I can't see it. Any further clues?
Kites

Posts: 48
Joined: 20 May 2005

The candidates for each cell in Column 3 are as follows:
6[78][134789][178][578][58][13479][347]2

Note that the values in the set {1, 3, 4, 9} are restricted to positions 3, 4, 6 and 7 in the column. We don't know which value will go into which cell - but it's possible to remove other candidates from these cells, which leaves us with:

6[78][1349]1[578][58][1349][34]2

We see that '1' goes into Row 4. The rest of the puzzles follows quickly.
Sue De Coq

Posts: 93
Joined: 01 April 2005

Or you might find it easier to notice that the cells in positions 2, 5 and 6 have to contain the numbers 5 7 and 8. It's the same thing, but looked at from a different angle, if you like. Certainly I find it easier to find them this way, but I suppose it's a matter of preference. Either way, the conclusion you reach is that you have a 1 in position 4.
PaulIQ164

Posts: 533
Joined: 16 July 2005

[quote="Sue De Coq"]The candidates for each cell in Column 3 are as follows:
6[78][134789][178][578][58][13479][347]2

Note that the values in the set {1, 3, 4, 9} are restricted to positions 3, 4, 6 and 7 in the column. We don't know which value will go into which cell - but it's possible to remove other candidates from these cells, which leaves us with:

6[78][1349]1[578][58][1349][34]2

We see that '1' goes into Row 4. The rest of the puzzles follows quickly.[/quote]

Thank you and PaulIQ164 very much. Your replies have been a great help.

May I also ask for a bit of advise? When it comes to puzzles like this one what does one look for first? How do you decide which column or row to start with? Any tips? I started by looking for X wings, was that correct? I do a feindish puzzle every day but got stuck on this one. Thanks again.
Kites

Posts: 48
Joined: 20 May 2005

Paul's Naked Triple is much easier (for me) to see than Sue's Hidden Quad. In fact, I find it hard to see that quad even when pointed out, and would be unlikely to discern it on my own by visual inspection. Any tips on how to spot them?

BTW, Sue's post has a typo, the quads are in positions 3, 4, 7 and 8, not 3, 4, 6 and 7.

Kites, I find it easier to first look for Naked Doubles, and then Naked Triples. If I'm still stalled, I will next hunt for X-Wings. Others may do it differently. Pappocom says the "Hards" in the Wash Post do not require X-Wings, but I personally used and needed one to solve this past Sunday's puzzle, I was stuck until I went that route. I do the pencilmarks by hand, not with software.

As to where to start looking, I really think you just have to develop the knack of scanning quickly, recognizing patterns, then homing in. Comes with practice. If I'm wrong, I'd like to know it!
Doyle

Posts: 61
Joined: 11 July 2005

Thanks for your comments Doyle. Putting names to the situations I had on this puzzle (Naked Triple and Hidden Quod) certainly helped me understand and relate to some solving notes I have been reading about them.
What does 'Hards' in the Post Wash mean?

[quote="Doyle"]Paul's Naked Triple is much easier (for me) to see than Sue's Hidden Quad. In fact, I find it hard to see that quad even when pointed out, and would be unlikely to discern it on my own by visual inspection. Any tips on how to spot them?

BTW, Sue's post has a typo, the quads are in positions 3, 4, 7 and 8, not 3, 4, 6 and 7.

Kites, I find it easier to first look for Naked Doubles, and then Naked Triples. If I'm still stalled, I will next hunt for X-Wings. Others may do it differently. Pappocom says the "Hards" in the Wash Post do not require X-Wings, but I personally used and needed one to solve this past Sunday's puzzle, I was stuck until I went that route. I do the pencilmarks by hand, not with software.

As to where to start looking, I really think you just have to develop the knack of scanning quickly, recognizing patterns, then homing in. Comes with practice. If I'm wrong, I'd like to know it![/quote]
Kites

Posts: 48
Joined: 20 May 2005

What does 'Hards' in the Post Wash mean?

The Washington Post newspaper publishes a daily Sudoku, from Pappocom. They get more difficult as the week goes on, and are each labeled as to difficulty. Currently, the one on Sunday is the most difficult and is labeled "Hard." I've read here on these boards that the newspaper puzzles just scratch the level of difficulty, and I do find that I can currently solve all the Hards, though I have to work at them. Pappocom (Wayne) posted once that X-Wings are not needed for the Hards, other, presumably simpler, techniques will suffice. However, my pencilmark system sort of makes them, some of them anyway, stand out, so I use them when I see them.
Doyle

Posts: 61
Joined: 11 July 2005