The New Sudoku Players' Forum

[kmart05]

I have been stuck on this puzzle for awhile and have browsed through this forum and couldn't find any other questions on it. Can you please give me a hint to help me finish?

1 _ _ l _ 8 _ l 9 _ _
_ _ 6 l _ _ 5 l _ 7 _
_ 9 _ l _ _ 4 l _ 1 _
---------------------
_ 4 _ l 7 _ _ l 8 5 _
_ 1 _ l _ 5 8 l _ _ _
8 6 5 l _ _ 2 l _ 3 _
----------------------
_ 7 _ l 8 _ _ l _ 6 _
_ 2 _ l 5 _ _ l 3 _ _
_ _ 1 l _ 2 _ l _ _ 4

I have found the answer on pappocom but don't know how I get it (Washington Post; 18965); let me know if it would be helpful to post the answer also.

Thank you very much!

[Shazbot]

from the original candidates:

Code: Select all

*-----------------------------------------------------------*
| 1     35   2347  | 236   8      367   | 9     24   2356   |
| 234   38   6     | 1239  139    5     | 24    7    238    |
| 2357  9    2378  | 236   367    4     | 256   1    23568  |
|------------------+--------------------+-------------------|
| 239   4    239   | 7     1369   1369  | 8     5    1269   |
| 2379  1    2379  | 3469  5      8     | 2467  249  2679   |
| 8     6    5     | 149   149    2     | 147   3    179    |
|------------------+--------------------+-------------------|
| 3459  7    349   | 8     1349   139   | 125   6    1259   |
| 469   2    489   | 5     14679  1679  | 3     89   1789   |
| 3569  358  1     | 369   2      3679  | 57    89   4      |
*-----------------------------------------------------------*


• in box 8, 4s can only go in column 5, so can be removed from r6c5
• 8 and 9 are the only candidates for r8c8 and r9c8, so those two numbers MUST go into those cells and can be removed from the rest of box 9 and also the rest of column 8 - this is called a naked pair
• 2 and 4 are the only candidates for r1c8 and r2c7 (another naked pair), so again can be removed from all other cells in box 3
• this presents another naked pair (3 and 8) in row 2, so those numbers can be eliminated from all other cells in that row
• gives another naked pair (1 and 9) in column 5
• there's an "x-wing" of 1s in columns 4 and 5 (the only two places they can go in those columns are in rows 2 and 6) so any other 1s in either of those rows can be removed
• this will allow you to place some 1s and will get you quite a bit further into the puzzle

if you can't complete from here, post again with the grid you've reached so far and you'll get more assistance

[Animator]

• there's an "x-wing" of 1s in columns 4 and 5 (the only two places they can go in those columns are in rows 2 and 6) so any other 1s in either of those rows can be removed

Theoretically this is an X-wing but I wouldn't call it one.

It simply is a case of locked candidates:

• the 1 in box 8 can only go in column 6: elimenate 1 as a candidate from r4c6.
• the only place for the number 1 in box 2 is on row 2. So remove all other 1s from row 2 that are not in box 2.
• the only place for the number 1 in box 5 is on row 6. So remove 1 as a candidate from r6c7 and r6c9.
  

[kmart05]

Thank you so much! I needed the 1s and 9s in column 5. I really appreciate your help!