The New Sudoku Players' Forum

[kit_carmelite]

I realize that because of the (4,5) pair in box 9, that I can remove the 4s and 5s from the other two cells in that box. I then have two cells with 4,5 and 2,7. But I don't know where to go from there. I've been away from Sudoku for a bit so it's probably something obvious I'm missing?

Original puzzle

Code: Select all

         
 *-----------*
 |..2|4..|6.9|
 |.4.|...|8..|
 |6.9|...|.1.|
 |---+---+---|
 |5..|6.9|..3|
 |.3.|.7.|.9.|
 |7..|5.3|..6|
 |---+---+---|
 |.6.|...|3.8|
 |..5|...|.6.|
 |9.7|..2|1..|
 *-----------*


Where I got stuck without pencil marks

Code: Select all

 *-----------*
 |8.2|4..|639|
 |143|..6|8..|
 |6.9|.3.|.1.|
 |---+---+---|
 |5..|6.9|..3|
 |.36|.7.|591|
 |79.|5.3|..6|
 |---+---+---|
 |.6.|...|3.8|
 |3.5|...|96.|
 |987|362|1..|
 *-----------*


Where I got stuck WITH pencil marks
[code]
{8} {57} {2} {4} {15} {157} {6} {3} {9}
{1} {4} {3} {279} {259} {6} {8} {257} {257}
{6} {57} {9} {278} {3} {578} {247} {1} {2457}
{5} {12} {148} {6} {1248} {9} {247} {2478} {3}
{24} {3} {6} {28} {7} {48} {5} {9} {1}
{7} {9} {148} {5} {1248} {3} {24} {248} {6}
{24} {6} {14} {179} {1459} {1457} {3} {2457} {8}
{3} {12} {5} {178} {148} {1478} {9} {6} {247}
{9} {8} {7} {3} {6} {2} {1} {45} {45}
/code]

[JasonLion]

There is a locked candidates direct pointing in block 5 -> column 5, allowing an immediate placement of a 1 in block 3. It is a little tricky to see without pencil marks, though not too bad.

[Marty R.]

Code: Select all

+-----------+---------------+---------------+
| 8  57 2   | 4   15   157  | 6   3    9    |
| 1  4  3   | 279 259  6    | 8   257  257  |
| 6  57 9   | 278 3    578  | 247 1    2457 |
+-----------+---------------+---------------+
| 5  12 148 | 6   1248 9    | 247 2478 3    |
| 24 3  6   | 28  7    48   | 5   9    1    |
| 7  9  148 | 5   1248 3    | 24  248  6    |
+-----------+---------------+---------------+
| 24 6  14  | 179 1459 1457 | 3   2457 8    |
| 3  12 5   | 178 148  1478 | 9   6    247  |
| 9  8  7   | 3   6    2    | 1   45   45   |
+-----------+---------------+---------------+


Play this puzzle online at the Daily Sudoku site

[David P Bird]

To supplement Jason's reply, I call the technique you seem to have forgotten box/line intersections. If there is only one box/line intersection a digit can occupy in a box (where it is considered to be locked) it can't be true elsewhere in the line, and vice versa. The placement for (1) he mentions is in box 2 not box 3 - an obvious typo.

[Pat]

Code: Select all


box\line:    (1) b5\c5 --> r1 1

or

line\box:    (1) c4\b8 --> c6 1



[kit_carmelite]

I clicked on the link to play the puzzle and when I asked for a hint, it placed a 5 in R1-C5. Then I understood what you were getting at about locked candidates. In box 5, a 1 can only go in R4-C5 or R6-C5 and therefore can't go anywhere else in C5. This gives an immediate placement of a 5 in R1-C5. Is this what you meant?

[kit_carmelite]

After following your suggestion (which places the 5, not the 1 in R1-C5), this is what I ended up with but I'm stuck again.
The only hint I get from Simple Sudoku highlights the 4 and 5 in box 9 and says "exclude based on naked pairs. I get that I should end up with the other two empty cells of box 9 having only 2 and 7 but I don't see where that helps me.
Puzzle withot pencil marks

Code: Select all

 *-----------*
 |872|451|639|
 |143|..6|8..|
 |659|.3.|.1.|
 |---+---+---|
 |5..|6.9|..3|
 |.36|.7.|591|
 |79.|5.3|..6|
 |---+---+---|
 |.6.|..5|3.8|
 |3.5|...|96.|
 |987|362|1..|
 *-----------*


Puzzle with pencil marks

Code: Select all

{8}    {7}    {2}    {4}    {5}    {1}    {6}    {3}    {9}   
{1}    {4}    {3}    {279}  {29}   {6}    {8}    {257}  {257} 
{6}    {5}    {9}    {278}  {3}    {78}   {247}  {1}    {247} 
{5}    {12}   {148}  {6}    {1248} {9}    {247}  {2478} {3}   
{24}   {3}    {6}    {28}   {7}    {48}   {5}    {9}    {1}   
{7}    {9}    {148}  {5}    {1248} {3}    {24}   {248}  {6}   
{24}   {6}    {14}   {179}  {149}  {5}    {3}    {27}  {8}   
{3}    {12}   {5}    {178}  {148}  {478}  {9}    {6}    {27} 
{9}    {8}    {7}    {3}    {6}    {2}    {1}    {45}   {45}   


[David P Bird]

There are more box/line eliminations to be had for digits 1, 4, and 8 in your reduced grid.

[Pat]

29 cells given
+ 15 "singles" —

Code: Select all


 8 . 2 | 4 . . | 6 3 9
 1 4 3 | . . 6 | 8 . .
 6 . 9 | . 3 . | . 1 .
-------+-------+------
 5 . . | 6 . 9 | . . 3
 . 3 6 | . 7 . | 5 9 1
 7 9 . | 5 . 3 | . . 6
-------+-------+------
 . 6 . | . . . | 3 . 8
 3 . 5 | . . . | 9 6 .
 9 8 7 | 3 6 2 | 1 . .



box\line (2 moves):

• (1) b5\c5
  
• (4) b7\r7
or

line\box (2 moves):

• (8) r5\b5
• (4) r9\b9

this should not need "pencilmarks"

[kit_carmelite]

I use Simple Sudoku which lets me export the puzzle with and without pencil marks.

I find what is below very cryptic. I don't understand this shorthand yet.

box\line (2 moves):
(1) b5\c5
(4) b7\r7
or

line\box (2 moves):
(8) r5\b5
(4) r9\b9

[7b53]

box/line = blr (box line reduction)
(8) r5\b5 = digit 8 row 5 \ box 5

Code: Select all

 *-----------*
 |872|451|639|
 |143|..6|8..|
 |659|.3.|.1.|
 |---+---+---|
 |5..|6.9|..3|
 |.36|.7.|591|
 |79.|5.3|..6|
 |---+---+---|
 |.6.|..5|3.8|
 |3.5|...|96.|
 |987|362|1..|
 *-----------*

your next move should be(digit 8) at row 5.
only two cells for it ( r5c4 or r5c6 ). both are within the same box.(box 5)
meaning r4c5 and r6c5 both cannot be an 8.
now look at column 5, there is only one cell left where you can place digit 8.

[kit_carmelite]

I must be missing something. I see 2 places for the 8 in column 5, rows 4 and 6'

If I understand your notation, the number in parentheses is the number to to placed in the puzzle?

If there are 3 possible places for a number, two of which are in the same box and row, why does that mean it can't go in one of those spots?

[7b53]

I see 2 places for the 8 in column 5, rows 4 and 6'

No, there are 3 places for the 8 in column 5, rows 4, 6, and row 8.

look at box 5;

Code: Select all

 *-----------*
 |872|451|639|
 |143|..6|8..|
 |659|.3.|.1.|
 |---+---+---|
 |5..|6.9|..3|
 |.36|x7x|591|
 |79.|5.3|..6|
 |---+---+---|
 |.6.|..5|3.8|
 |3.5|...|96.|
 |987|362|1..|
 *-----------*   

 one of the cell marked "x" must be an 8.


Code: Select all

 *-----------*
 |872|451|639|
 |143|..6|8..|
 |659|.3.|.1.|
 |---+---+---|
 |5..|6y9|..3|
 |.36|.7.|591|
 |79.|5y3|..6|
 |---+---+---|
 |.6.|..5|3.8|
 |3.5|...|96.|
 |987|362|1..|
 *-----------*

can the cells marked with "y" be an 8 ?


answer is no. otherwise there is no place for digit 8 at row 5.
so for column 5, only cell left is at row 8.
r8c5=8 (row 8/column 5 equal to 8).

please don't get the row, column mix up !
hope you understand this better.

[Pat]

box\line (2 moves):

• (1) b5\c5
  
• (4) b7\r7
or

line\box (2 moves):

• (8) r5\b5
• (4) r9\b9

I don't understand this shorthand yet.

box/line = blr (box line reduction)
(8) r5\b5 = digit 8 row 5 \ box 5

your next move should be (digit 8) at row 5.
only two cells for it ( r5c4 or r5c6 ). both are within the same box (box 5).
meaning r4c5 and r6c5 cannot be an 8.
now look at column 5,
there is only one cell left where you can place digit 8.

so my post was too brief
thanks to 7b53 for providing the missing explanation

historical note:
for the backslash shorthand,
credit ronk ( link to old post 2006.Nov.17 )

. - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . -
box\line example:
(4) b7\r7

observation:
the 4 for b7 can only be in r7
conclusion:
exclude 4 elsewhere in r7

. - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . -
line\box example:
(4) r9\b9

observation:
the 4 for r9 can only be in b9
conclusion:
exclude 4 elsewhere in b9

. - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . -
the above 2 examples are similar but not equivalent —
one provides exclusions in r7, the other in b9