The New Sudoku Players' Forum

[David B]

I seldom fail to solve the problems in the Times each day but the Friday fiendish seem to take me longer and longer.

On puzzle 862 I have given as much time as I want to and have only inserted 7 numbers. I'm obviously missing something


1 x x x x 8 3 x x
x x 8 x 7 2 6 1 x
x x x 1 3 9 4 x 8

x x x x 9 x 7 x x
7 x x x x x x x 2
x x 9 x 5 7 x x x

x x 7 x 8 x 2 x x
x 4 8 9 2 x 3 7 x
x x 2 7 x x x x 4

[QBasicMac]

Well, the 7 at r1c9 is fairly easy to spot. Then the 7 at r3c2.

But then I see your point.

Mac

[emm]

Hi David

One thing you're missing is the correct grid - you have 2 8s in c3 and 2 3s in c7.

Here is your puzzle entered into Simple Sudoku .

This is an excellent solver and hint provider if you're interested.

Code: Select all

 *-----------*
 |1..|..8|3..|
 |.8.|.72|61.|
 |...|139|4.8|
 |---+---+---|
 |...|.9.|7..|
 |7..|...|..2|
 |..9|.57|...|
 |---+---+---|
 |..7|.8.|2..|
 |.48|92.|.37|
 |..2|7..|..4|
 *-----------*

Code: Select all

*-----------------------------------------------------------------------------*
 | 1       25679   456     | 456     46      8       | 3       27      59      |
 | 3459    8       345     | 45      7       2       | 6       1       59      |
 | 256     2567    56      | 1       3       9       | 4       27      8       |
 |-------------------------+-------------------------+-------------------------|
 | 234568  12356   13456   | 23468   9       1346    | 7       4568    1356    |
 | 7       1356    13456   | 3468    146     1346    | 1589    45689   2       |
 | 23468   1236    9       | 23468   5       7       | 18      468     136     |
 |-------------------------+-------------------------+-------------------------|
 | 3569    13569   7       | 3456    8       13456   | 2       569     1569    |
 | 56      4       8       | 9       2       156     | 15      3       7       |
 | 3569    13569   2       | 7       16      1356    | 1589    5689    4       |
 *-----------------------------------------------------------------------------*

Naked pair

Locked candidates

Singles

[David B]

One thing you're missing is the correct grid - you have 2 8s in c3 and 2 3s in c7.

Many thanks, you are quite right, I put a space in the wrong place in row 2.

You have entered the puzzle quite correctly but it doesn't seem to take me further, Your program states.

Naked pair

Locked candidates

Singles

I had already seen the pairs 27 in c8 an 59 in c9 but they don't lead me anywhere.

I use a Mac and don't have a program which gives hints, I can get a solution but I am only interested in HOW to solve it.

Any further ideas?

[Cec]

I use a Mac and don't have a program which gives hints, I can get a solution but I am only interested in HOW to solve it.
Any further ideas?

The program solver suggested by emm above provides hints plus many other useful aids for solving puzzles. If you want to know more about this program just click on Here .

More about solving techniques can be found by clicking the following links:

http://www.angusj.com/sudoku/hints.php
http://www.sadmansoftware.com/sudoku/techniques.htm
http://www.scanraid.com/BasicStrategies.htm

Cec

[Cec]

"..I had already seen the pairs 27 in c8 an 59 in c9 but they don't lead me anywhere..."

Sorry DavidB .. I overlooked your other query and hopefully this will help...

Yes, the naked pairs [27] and [59] don't lead to much apart from excluding the other candidates 5 and 9 in the remainder of column9.

The above angusj link explains the "Locked Candidates" (1) and (2) solving techniques. As an example in your puzzle, in Box2 (the upper middle 3X3 grid) notice the 5's only appear in column 4 (c4). This means any other 5's outside this Box2 can be excluded from c4. Also in Box2, the 6's occur only in row1 (r1). This means all other 6's outside this box can be excluded from r1.

Try spotting other "Locked Candidates " in Box 7 (lower left 3X3 grid)..(candidate 1's) and also in Box 1 (candidate 5's)

Cec

[David B]

Thanks Cec, I'll have another look, I had spotted some of these locked pairs but they didn't seem to lead me anywhere. I will try again.

I don't tend to note all possibilities in a workbox but mark every occurence of what i call "exclusive pairs" in each 3 x 3 box.

[Cec]

".. I had spotted some of these locked pairs but they didn't seem to lead me anywhere. I will try again...."

I'm not familiar with your reference to "locked pairs". If you're still stuck after trying, the four occurrences of "Locked Candidates" I mentioned above should lead to the exclusion of candidates as follows:

Locked Candidates 5 in c4 Box2.. exclude candidate 5 from r7c4
Locked Candidates 6 in r1 Box2.. exclude candidate 6's from r1c23
Locked Candidates 1 in c2 Box7.. exclude candidate 1's from c2r456
Locked Candidates 5 in r3 Box1.. exclude candidate 5's from r1c23 and r2c13.

After the above exclusions, only naked and hidden singles are left to solve this puzzle.

Cec

[David B]

[
The above angusj link explains the "Locked Candidates"

I had already found the locked pairs you identified, coming back to the puzzle after a long break and reading the angusj reference I see that in R1 C 345 I have what he calls

xy-wing pattern shared the same group, [then they would be] called a 'naked triple

I haven't yet looked at the implications rather than putting a 9 in R1C9 and 5 in R2C9.

Hopefully this is the breakthrough.

[David B]

Locked Candidates 5 in c4 Box2.. exclude candidate 5 from r7c4
Locked Candidates 6 in r1 Box2.. exclude candidate 6's from r1c23
Locked Candidates 1 in c2 Box7.. exclude candidate 1's from c2r456

Locked Candidates 5 in r3 Box1.. exclude candidate 5's from r1c23 and r2c13.

After the above exclusions, only naked and hidden singles are left to solve this puzzle.

My last message was posted before I read your last one, I had already spotted the first three hints but had missed the fourth one which gives a 4 in R1C3 and then resolves the same triple as I found by a long winded route.

Your Locked Candidates had been staring me in the face all the times and are a much more elegant solution.

Many thanks

[David B]

Locked Candidates 5 in r3 Box1.. exclude candidate 5's from r1c23 and r2c13.

After the above exclusions, only naked and hidden singles are left to solve this puzzle.

After that "triple" the whole puzzle fell into place in a minute or so. Thanks again.

[Cec]

"....Your Locked Candidates had been staring me in the face all the times and are a much more elegant solution...."

By way of interest, the following is an alternative solution which I didn't spot initially:

There is a naked triple [456] in r1 which leads to a "bucket load" of naked singles as follows:
r1c9 =9
r2c9 =5
r2c4 =4
r2c3 =3
r1c4 =5
r1c3 =4
r2c1 =9
r9c5 =1
r5c5 =4

After placing the above singles, many basic exclusions result including another naked triple [356] in c1 (Box7) which, from further basic exclusions, leaves only naked singles to solve the puzzle. If you did spot this naked triple then I apologise for repeating what you detected.

As I recall, another member pointed out in another thread sometime back "there's more than one way to skin a cat" and this puzzle is such an example. Anyway, the "Locked Candidates" alternative is a valuable technique to learn when other alternatives are not available.

BTW, I'm still not sure what you mean by "Locked Pairs"

Cec

[Sheldon Wu]

"....Your Locked Candidates had been staring me in the face all the times and are a much more elegant solution...."

By way of interest, the following is an alternative solution which I didn't spot initially:

There is a naked triple [456] in r1 which leads to a "bucket load" of naked singles as follows:
r1c9 =9
r2c9 =5
r2c4 =4
r2c3 =3
r1c4 =5
r1c3 =4
r2c1 =9
r9c5 =1
r5c5 =4

After placing the above singles, many basic exclusions result including another naked triple [356] in c1 (Box7) which, from further basic exclusions, leaves only naked singles to solve the puzzle. If you did spot this naked triple then I apologise for repeating what you detected.

As I recall, another member pointed out in another thread sometime back "there's more than one way to skin a cat" and this puzzle is such an example. Anyway, the "Locked Candidates" alternative is a valuable technique to learn when other alternatives are not available.

BTW, I'm still not sure what you mean by "Locked Pairs"

Cec

[Cec]

Hi Sheldon Wu,

If you want to post a message, scroll up to the start of this thread and click on "Post reply" display button. A "Post a reply" blank window box opens up for you to type your message. Click Preview button to check how your message looks and if OK then click on "Submit" button

Cec