I found a cool uniqueness move, an x-wing and finally a forcing chain to solve this puzzle
My walkthrough:
1. NP {28} in N5 -> r4c4=6 -> NP {39} in c6/N5 -> r1c6 = 1/6/7
2. NT {147} in c6/N8 -> r1c6 = 6, r9c4 = 2/5/8
3. NP {57} in c4/N2 -> r1c4 = 1, r23c5 = {39}, r9c4 = 2/8
4. HS r6c6 = 3, r4c6 = 9
5. Grid now:
Code: Select all
*-----------------------------------------------------------------------------*
| 2 379 3579 | 1 4 6 | 35 79 8 |
| 457 3479 1 | 57 39 8 | 2 4679 4569 |
| 4578 6 345789 | 57 39 2 | 345 1 459 |
|-------------------------+-------------------------+-------------------------|
| 48 234 348 | 6 1 9 | 7 5 249 |
| 9 127 78 | 4 28 5 | 168 268 3 |
| 148 5 6 | 28 7 3 | 148 2489 1249 |
|-------------------------+-------------------------+-------------------------|
| 14567 8 457 | 9 25 147 | 1456 3 12456 |
| 14567 147 2 | 3 58 147 | 9 468 1456 |
| 3 149 459 | 28 6 14 | 1458 248 7 |
*-----------------------------------------------------------------------------*
Either r2c1 = 4 or r3c1 = 4 or 8.
Since r4c1 = 4/8, 4 and 8 cannot go elsewhere in c1 -> r6c1 = 1 -> r78c1 = {567}
6. NT {278} in r5c235 -> r5c8 = 6, r5c7 = 1
7. 8 locked to r6 in N6 -> r6c4 = 2 -> several naked and hidden singles to here:
Code: Select all
*--------------------------------------------------------------------*
| 2 379 359 | 1 4 6 | 35 79 8 |
| 457 3479 1 | 57 39 8 | 2 479 6 |
| 4578 6 34589 | 57 39 2 | 345 1 459 |
|----------------------+----------------------+----------------------|
| 48 34 348 | 6 1 9 | 7 5 2 |
| 9 2 7 | 4 8 5 | 1 6 3 |
| 1 5 6 | 2 7 3 | 8 49 49 |
|----------------------+----------------------+----------------------|
| 57 8 45 | 9 2 147 | 6 3 145 |
| 6 147 2 | 3 5 147 | 9 8 14 |
| 3 149 459 | 8 6 14 | 45 2 7 |
*--------------------------------------------------------------------*
9. Forcing chain:
If r7c6 = 1 -> r9c6 = 4, r9c7 = 5, r9c3 = 9, r9c2 = 1, r8c2 = 7
If r7c6 = 7 -> r7c1 = 5, r9c3 = 9, r9c2 = 1, r8c2 = 7
The rest is singles.