You weren't able to make any placements? I presume you don't use pencilmarks.

OK, Look at cell r4c5. (Row 4 is the 4th from the top, Column 5 is the fifth from the left. We call that r4c5.)

Can a 1 go there? No, because there is already a 1 in r5c6 (same box)

Can a 2 go there? No, because there is already a 2 in r4c8 (same row)

Can a 3 go there? No, because there is already a 3 in r5c4 (same box)

Can a 4 go there? Yes

Can a 5 go there? No, because there is already a 5 in r6c6 (same box)

Can a 6 go there? No, because there is already a 6 in r4c4 (same row)

Can a 7 go there? No, because there is already a 7 in r4c3 (same row)

Can a 8 go there? No, because there is already a 8 in r7c5 (same column)

Can a 9 go there? No, because there is already a 9 in r4c2 (same row)

OK, since only one candidate can go there, you can confidently write a 4 in r4c5.

How did I know to examine that cell? A hunch because of all the numbers in the row, box and column it fell in. I could have been unlucky and found two candidates. But I would keep looking.

Now we have the 4 placed. As a result it turns out that r6c5 has only one legal candidate now: 2. So we place a 2 in r6c5. The notation for that is

r6c5=2

Continuing: r6c4=9, r5c5=7, r4c6=8.

You get the idea. Keep doing that and you will get stuck here

- Code: Select all
`9-3 1-- ---`

54- --- ---

6-- -9- ---

197 648 325

--5 371 469

436 925 781

--- -8- --7

--- --- -56

7-- --2 8-3

Well, finally I would notice that there is a 2 and 8 in columns 5 and 6.

So column 4 in the top box (box 2) must have 2 and 8 also, right? Luckily there is already a 1 in r1c4 so we are confident that there is a 2 or 8 in r2c4 and r3c4.

So the other cells in that box must have 123456789-1289=34567, right? But I can't see any benefit of knowing that at this time. I'd say 80% of my hunches go nowhere.

Ok, try looking at the bottom of column c4. It must have 123456789-128639=457

But I see that row 7 already has a 7 at r7c9.

And row 9 has a 7 at r9c1.

That was lucky. That means the 7 in 457 must go in r8c5!

Put it there.

Errk! That is the way I usually solve puzzles, but I also choose easier puzzles than you have. I can't easily see what to do next.

You should learn about pencilmarks to do puzzles like this. If you want, I'm sure someone will post pencilmarks and show some further steps.

Pencilmarks at this point are

- Code: Select all
`+------------------+-----------------+-----------------+`

| 9 278 3 | 1 56 467 | 256 47 248 |

| 5 4 128 | 28 36 367 | 1269 1379 28 |

| 6 1278 128 | 2458 9 347 | 125 1347 248 |

+------------------+-----------------+-----------------+

| 1 9 7 | 6 4 8 | 3 2 5 |

| 28 28 5 | 3 7 1 | 4 6 9 |

| 4 3 6 | 9 2 5 | 7 8 1 |

+------------------+-----------------+-----------------+

| 23 1256 1249 | 45 8 3469 | 129 149 7 |

| 238 128 12489 | 7 13 349 | 129 5 6 |

| 7 156 149 | 45 156 2 | 8 149 3 |

+------------------+-----------------+-----------------+

Mac