Diagonal Sudoku - Free Printable

Let's solve this Sudoku puzzle step by step.

Step 1: Understand the Puzzle

We are given a 9×9 Sudoku grid with some numbers already filled in. The goal is to fill in the empty cells so that each row, each column, and each of the nine 3×3 subgrids (also called "boxes") contains all of the digits from 1 to 9 without repetition.

Here’s the initial grid:

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

We'll label rows from top to bottom as R1 to R9, and columns from left to right as C1 to C9. Each 3×3 box will be labeled B1 to B9.

---

Step 2: Start Solving

We'll use logical deduction — look for cells where only one number can go based on row, column, and box constraints.

#### Look at R1C1:
- R1 has: 8, 9, 5, 4 → missing: 1, 2, 3, 6, 7
- C1 has: ?, ?, ?, 1, 3, ?, 5, ?, ? → values: 1, 3, 5 → missing: 2,4,6,7,8,9
- B1 (top-left 3×3): R1C1–R3C3 → currently: 8,9,5,4,6,7 → missing: 1,2,3

So R1C1 must be in {1,2,3} ∩ {2,4,6,7,8,9} ∩ {1,2,3} = {1,2,3}

But we need more info.

Wait — let's go to R2C9:
- R2: ?, ?, ?, ?, ?, ?, ?, ?, 9 → so missing: 1–8
- C9: ?, 9, ?, 4, 3, 6, ?, 5, 9 → wait, R2C9 = 9, R4C9 = 4, R5C9 = 3, R6C9 = 6, R8C9 = 5, R9C9 = 9? Wait no, R9C9 isn't set yet.

Wait — let's reconstruct the full grid properly.

Let me write the grid clearly:

```
Row 1: 8 9 _ | 5 4 _ | _ _ _
Row 2: _ _ _ | _ _ _ | _ _ 9
Row 3: _ _ _ | _ 7 _ | _ _ _
+-------+-------+-------+
Row 4: _ 6 _ | _ 2 _ | _ _ 4
Row 5: 1 _ _ | 4 _ _ | _ _ 3
Row 6: 3 _ _ | 7 _ 6 | _ _ _
+-------+-------+-------+
Row 7: _ 5 _ | 6 _ _ | _ _ _
Row 8: _ _ _ | 4 1 _ | 5 9 _
Row 9: _ _ _ | _ _ _ | _ _ _
```

Now, let’s denote each cell.

---

Step 3: Focus on Box 5 (center box: R4C4 to R6C6)

Box 5:
```
_ 2 _
4 _ _
7 _ 6
```

So:
- Missing numbers: 1,3,5,8,9

Let’s look at R5C5: it's blank.
- R5: 1, _, _, 4, _, _, _, _, 3 → missing: 2,5,6,7,8,9
- C5: 4, ?, 7, 2, ?, ?, ?, 1, ? → current: 4,7,2,1 → missing: 3,5,6,8,9
- So R5C5 ∈ {2,5,6,7,8,9} ∩ {3,5,6,8,9} = {5,6,8,9}

But also, Box 5 has:
- R4C4: ?, R4C5: 2, R4C6: ?
- R5C4: 4, R5C5: ?, R5C6: ?
- R6C4: 7, R6C5: ?, R6C6: 6

So Box 5 missing: 1,3,5,8,9

Now, R4C4: possible?
- R4: ?, 6, ?, ?, 2, ?, ?, ?, 4 → missing: 1,3,5,7,8,9
- C4: 5, ?, ?, ?, 4, 7, 6, 4, ? → wait: R1C4=5, R2C4=?, R3C4=?, R4C4=?, R5C4=4, R6C4=7, R7C4=6, R8C4=4, R9C4=?

So C4: 5, ?, ?, ?, 4, 7, 6, 4, ? → duplicates: 4 appears twice (R5C4 and R8C4) → that’s okay if they’re different rows.

But wait — R8C4 = 4, R5C4 = 4 → same column → conflict? No, same column, but different rows → allowed only if not same cell.

Wait — R5C4 = 4, R8C4 = 4 → same column → both have 4 → okay, but now C4 has two 4s? That would be invalid.

Wait — let's check:

- R5C4 = 4 (given)
- R8C4 = 4 (given)

Yes, both are in C4 → so C4 has two 4s → invalid unless it's a mistake.

Wait — no! Let's recheck the original image.

Looking back at your image:

> Row 5: 1 | 4 | 3 |

So R5C4 = 4

Row 8: | 4 1 | 5 9 |

So R8C4 = 4

Yes — so C4 has R5C4 = 4 and R8C4 = 4 → same column → duplicate → impossible.

Wait — that can't be. Unless I misread.

Wait — perhaps the image has a typo? Or did I misplace?

Let me double-check the original image you provided.

You wrote:

```
8 9 | 5 4 |
| | 9
| 7 |

6 | 2 | 4
1 | 4 | 3
3 | 7 | 6

5 | 6 |
| 4 1 | 5 9
| |
```

So:

- R5: 1 _ _ | 4 _ _ | _ _ 3 → so R5C4 = 4
- R8: _ _ _ | 4 1 _ | 5 9 _ → so R8C4 = 4

Yes — both R5C4 and R8C4 are 4 → same column → duplicate → invalid.

But that can't happen in a valid Sudoku.

Unless... is there a mistake in reading?

Wait — maybe the line break is wrong.

Look at the image: it says:

```
1 | 4 | 3
```

That’s R5.

Then:

```
3 | 7 | 6
```

R6.

Then:

```
5 | 6 |
```

R7: C2=5, C4=6

Then:

```
| 4 1 | 5 9
```

R8: C4=4, C5=1, C7=5, C8=9

Yes — so R8C4 = 4

And R5C4 = 4

Same column → two 4s → invalid.

But that suggests the puzzle is invalid.

Wait — perhaps I misread R5C4.

Let’s list the grid again carefully.

From your input:

Row 1: 8 9 _ | 5 4 _ | _ _ _

Row 2: _ _ _ | _ _ _ | _ _ 9

Row 3: _ _ _ | _ 7 _ | _ _ _

Row 4: _ 6 _ | _ 2 _ | _ _ 4

Row 5: 1 _ _ | 4 _ _ | _ _ 3

Row 6: 3 _ _ | 7 _ 6 | _ _ _

Row 7: _ 5 _ | 6 _ _ | _ _ _

Row 8: _ _ _ | 4 1 _ | 5 9 _

Row 9: _ _ _ | _ _ _ | _ _ _

So:

- C4: R1C4=5, R2C4=?, R3C4=?, R4C4=?, R5C4=4, R6C4=7, R7C4=6, R8C4=4, R9C4=?

So R5C4 = 4, R8C4 = 4 → both in C4 → duplicate → invalid

Therefore, the puzzle as given has a contradiction.

But that can’t be — probably I made a mistake in interpretation.

Wait — could R8C4 be something else?

Look at the text:

```
| 4 1 | 5 9
```

The first part is " |" which is three blanks before the pipe.

So:

- C1: blank
- C2: blank
- C3: blank
- C4: 4
- C5: 1
- C6: blank
- C7: 5
- C8: 9
- C9: blank

Yes → R8C4 = 4

And R5C4 = 4 → same column → impossible.

So either the puzzle is invalid, or I've misread.

Wait — perhaps the line for R5 is:

"1 | 4 | 3"

So R5C1=1, R5C4=4, R5C9=3 → yes.

And R8C4=4 → conflict.

So unless the puzzle has a typo, it's unsolvable.

But maybe the website watermark is obscuring something?

It says: "www.4pe.net" — perhaps the numbers are misaligned?

Wait — look at the image structure:

There are 9x9 cells, with bold lines every 3 columns and 3 rows.

In your ASCII art:

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

Let’s count the characters.

Each cell is separated by spaces.

For example, first row: `| 8 9 | 5 4 | |`

So:

- C1: 8
- C2: 9
- C3: blank
- C4: 5
- C5: 4
- C6: blank
- C7: blank
- C8: blank
- C9: blank

Similarly, second row: `| | | 9 |` → C7=9

Third row: `| | 7 | |` → C5=7

Fourth row: `| 6 | 2 | 4 |` → C2=6, C5=2, C8=4

Fifth row: `| 1 | 4 | 3 |` → C1=1, C4=4, C9=3

Sixth row: `| 3 | 7 | 6 |` → C1=3, C4=7, C6=6

Seventh row: `| 5 | 6 | |` → C2=5, C4=6

Eighth row: `| | 4 1 | 5 9 |` → C4=4, C5=1, C7=5, C8=9

Ninth row: `| | | |` → all blank

So now let's extract the full grid:

```
Row 1: 8 9 _ | 5 4 _ | _ _ _
Row 2: _ _ _ | _ _ _ | _ _ 9
Row 3: _ _ _ | _ 7 _ | _ _ _
Row 4: _ 6 _ | _ 2 _ | _ _ 4
Row 5: 1 _ _ | 4 _ _ | _ _ 3
Row 6: 3 _ _ | 7 _ 6 | _ _ _
Row 7: _ 5 _ | 6 _ _ | _ _ _
Row 8: _ _ _ | 4 1 _ | 5 9 _
Row 9: _ _ _ | _ _ _ | _ _ _
```

Now, C4:
- R1C4 = 5
- R2C4 = ?
- R3C4 = ?
- R4C4 = ?
- R5C4 = 4
- R6C4 = 7
- R7C4 = 6
- R8C4 = 4 ← here!
- R9C4 = ?

So R5C4 = 4, R8C4 = 4 → both in column 4 → two 4s in same column → violates Sudoku rules.

Therefore, this puzzle is invalid as given.

But perhaps there is a typo in the image.

Wait — maybe R8C4 is not 4? Let's see the eighth row: `| | 4 1 | 5 9 |`

The first block is three blanks, then `| 4 1 |` → so C4=4, C5=1

Yes.

Unless the "4" in R8C4 is actually meant to be in a different position?

Or perhaps the puzzle has a mistake.

Alternatively, maybe the "4" in R5C4 is not there?

But R5: `| 1 | 4 | 3 |` → clearly shows 4 in the middle block, which is C4.

So R5C4 = 4

R8C4 = 4

Same column → invalid.

Therefore, the puzzle as presented contains an error.

But since you asked to solve it, perhaps it's a transcription error.

Wait — maybe the "4" in R8C4 is not a digit but part of the watermark?

Look: the watermark says "www.4pe.net" — and it's placed over the center.

In your image, the center cell (R5C5) has a diamond and "www.4pe.net" — so likely the "4" in the watermark is overlapping R5C5.

But in our grid, R5C5 is blank.

But R8C4 is separate.

Perhaps the "4" in R8C4 is actually the "4" from "4pe", but it's positioned at R8C4.

But visually, if the watermark is centered, it might be over R5C5.

But in your ASCII, you have:

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

And the watermark is written as "www.4pe.net" — possibly overlaid on the center.

But in the third row of the grid, you have:

```
| | 7 | |
```

Then:

```
| 6 | 2 | 4 |
```

Then:

```
| 1 | 4 | 3 |
```

Then:

```
| 3 | 7 | 6 |
```

Then:

```
| 5 | 6 | |
```

Then:

```
| | 4 1 | 5 9 |
```

So the "4" in "4 1" is at R8C4.

But if the watermark "4pe" is meant to be over R5C5, then perhaps the "4" in R8C4 is not part of the puzzle?

But that doesn't make sense.

Alternatively, maybe the "4" in R5C4 is not there.

Wait — let's assume that the "4" in R8C4 is a mistake, and it should be something else.

But without knowing what it should be, we can't proceed.

Alternatively, perhaps the puzzle is solvable if we ignore the conflict.

But it's not.

Another possibility: the "4" in R5C4 is not 4, but the "4" in the watermark is confusing.

But in the ASCII, it's clearly written as `| 4 |` in R5.

So unless there's a typo in the puzzle, it's unsolvable.

Wait — perhaps R5C4 is not 4, but the number is missing.

No — it's explicitly shown.

Wait — let's try to find a way around.

Maybe the "4" in R8C4 is not a digit, but the watermark's "4" is placed there.

But the watermark is "www.4pe.net" — likely centered over the center cell.

In a 9x9 grid, center is R5C5.

So the "4" in "4pe" is over R5C5.

But in your ASCII, you have:

```
| 1 | 4 | 3 |
```

So R5C4 = 4

But if the watermark is over R5C5, then the "4" in the watermark might be intended to be in R5C5, but it's written as part of the grid.

But in the text, it's `| 4 |` — which is C4.

So it's ambiguous.

Perhaps the correct value is in R5C5, not R5C4.

Let me re-express the fifth row:

"1 | 4 | 3 "

This means:
- First block: C1=1, C2=?, C3=?
- Second block: C4=4, C5=?, C6=?
- Third block: C7=?, C8=?, C9=3

So R5C4 = 4

But if the watermark is over R5C5, then the "4" might be intended for R5C5.

But in the text, it's not.

Alternatively, maybe the puzzle has a typo, and R8C4 should be 8 or something else.

But without clarification, we cannot proceed.

However, let's assume that the "4" in R8C4 is a mistake, and it should be another number.

But that's speculative.

Alternatively, perhaps the "4" in R5C4 is not there.

But it is.

Another idea: maybe the "4" in R8C4 is not a digit, but part of the watermark.

But it's in the cell.

Given the ambiguity, and since the puzzle has a clear conflict, I suspect there is a typo.

But let's try to solve it assuming R8C4 is not 4, but something else.

But we don't know what.

Alternatively, perhaps the "4" in R5C4 is not 4, but the watermark's "4" is meant to be in R5C5.

Let's suppose that the "4" in the second block of R5 is not in C4, but in C5.

But the block is `| 4 |` — which is three cells: C4, C5, C6.

If it's written as "4 ", it could mean C4=4, C5=?, C6=?

Yes.

But if the watermark is "4pe.net", and it's over R5C5, then perhaps the "4" is in R5C5.

But in the text, it's not specified.

Perhaps the correct grid has R5C5 = 4, and R5C4 is not 4.

But in the text, it's `| 4 |`, which suggests C4=4.

This is very ambiguous.

To resolve this, let's assume that the "4" in the watermark is meant to be in R5C5, and the "4" in R5C4 is a typo.

So let's assume that R5C4 is not 4, but the "4" in the second block of R5 is actually in C5.

But the text says `| 4 |` — which is C4=4.

Alternatively, maybe the grid is:

Row 5: 1 _ _ | _ 4 _ | _ _ 3

Then R5C5 = 4

And R8C4 = 4 — still conflict.

No.

Unless R8C4 is not 4.

But it is.

Perhaps the puzzle is from a source where the watermark is not part of the puzzle, and the "4" in R8C4 is a mistake.

But without more information, I can't solve it.

Given the time, perhaps you can double-check the image.

But based on the given text, the puzzle has a duplicate 4 in column 4 (R5C4 and R8C4), making it unsolvable.

Therefore, the puzzle as given is invalid due to a duplicate in column 4.

Please verify the original image or provide a corrected version.

If you can confirm the correct values, I can help solve it.