SudoCue Users

[sudokuEd]

Hi everyone,
One of the many things I enjoy about Easter is the memory of this classic killer by Nate Dorward. I spent Easter '06 trying to solve this beauty and have been hopelessly hooked on (difficult) killers ever since.

It hasn't been posted here before and so really wanted to share it with you now. If you enjoy/hate this horror ( ) and tell us about it, maybe we can encourage him to come out of puzzle retirement and make another new one for us.

Note - Nate has a walk-through with some alternative endings on his blog here. If someone finds a better way through, please publish!!

I tried to make a background image based on the classic 1968 movie - but...you'll just have to imagine the tombstone...

nd's #9 (aka Night of the Living Sudoku) SS(v3)score 2.45 (NOTE: no t&e)



PS code:
3x3::k:2816:2816:5378:2307:6660:6660:6660:6151:6151:2816:5378:5378:2307:6413:6660:7183:7183:6151:2834:3859:2836:2307:6413:7183:7183:6151:6151:2834:3859:2836:4126:6413:6413:7183:7202:7202:2834:5413:2836:4126:6413:6413:5930:5930:7202:5413:5413:4126:4126:6705:5938:5938:5930:7202:8502:5413:7736:6705:6705:6705:5938:5930:5930:8502:8502:7736:7736:7736:7736:5938:5938:6215:8502:8502:8502:8502:6215:6215:6215:6215:6215:

Thanks to nd for letting us have it published here.
Ed

[Afmob]

This was an interesting Killer since you could totally ignore some nonets to crack it which is the reason why my wt is quite short since I only used those "useless" nonets in the endgame.
At first I wanted to rate it 1.75 but I discovered that the complex combo analysis I had used wasn't necessary to solve it so I deleted it from my wt.

The overlap technique (step 2 from the blog) is quite useful in this Killer though you can come to the same results with more but easier moves.

I don't know why the SS rating so high (nearly off by 1.0!), maybe the X-Chain and techniques in the "useless" areas which SudokuSolver used, raised it so high.

ND's #9 Walkthrough:

1. C1234
a) Innies = 32(2+2) <> 1,2,3,4,5; R7C4 <> 6,7
b) Innies+Outies C4 : -20 = R6C3 - R789C4 -> R6C3 = (1234); R9C4 <> 1,2,3
c) Innies+Outies N14: R6C3 = R7C2 = (1234)
d) 30(5) = 89{157/247/256/346} because of step 1a
-> 8,9 locked between R8+N7 -> R8C12 <> 8,9
-> R8C56 = (12345)
e) Innies N1 = 13(3): R3C13 <> 6,7,8 because R3C2 >= 6
f) 5 locked in 33(7) @ N7 = 12567{39/48} -> 1,2 locked for N7
g) Innies+Outies N14: R6C3 = R7C2 = (34)
h) Innies+Outies C4 : -20 = R6C3 - R789C4 -> R789C4 = 23/24(3) = 89{6/7}
-> 8,9 locked for C4+N8
i) Innies+Outies C12: 1 = R9C34 - R2C2
-> R2C2 <> 4,5 because R9C34 >= 7
-> R9C3 = (1234) because R9C4 >= 6
j) 9(3) = 3{15/24} because {126} blocked by Killer pair (12) of 16(4) -> 3 locked for C4+N2

2. R789
a) Outies R9 = 12(3+1) -> R7C1+R8C9 <> 7,8,9
b) Hidden Killer pair (89) in 24(6) for R9 since 33(7) can't have both
-> 24(6) = 1234{59/68}
c) 7 locked in 33(7) @ R9 -> R8C12 <> 7
d) Killer quad (1234) locked in 24(6) + R9C3 for R9
e) 24(6) must have one of (1234) @ R8C9 (step 3d) -> R8C9 <> 5,6
f) Outies R9 = 12(3+1): R7C1 <> 5,6 since 12{3/4} are Killer triples of 30(5)
g) R8C9 <> 1 since it sees all 1 of N8
h) 24(6) = 1234{59/68} -> 1 locked for R9

3. C123 !
a) ! Hidden Killer quad (1234) in R18C2 for C2 since 21(4) can only have two of (1234)
-> R18C2 <> 5,6,7,8
b) 21(4) must have two of (1234) @ C2 -> R6C1 <> 1,2,3,4
c) Naked quad (1234) locked in R7C12+R8C2+R9C3 for N7
d) 1 locked in 11(3) @ C3 = 1{28/37/46} <> 5
e) 5 locked in 21(3) @ C3 = {579} locked for N1
f) 15(2): R4C2 <> 6,8
g) Naked pair (79) locked in R24C2 for C2

4. R123 !
a) ! Consider combos of 15(2) -> 11(3) @ R3C1 <> 7:
- i) 15(2) = [69] -> Innies N1 = {346} -> 1 locked in 11(3) @ C3 for N2 -> 11(3) @ R3C1 <> 1
- ii) 15(2) = [87] -> 11(3) <> {137}
b) Hidden pair (79) in R69C1 for C1 -> R69C1 <> 5,6,8
c) Naked pair (79) locked in R4C2+R6C1 for N4
d) 11(3) @ C3 = 1{28/46}
e) Innies+Outies C1: -23 = R1C2 - R6789C1 -> R7C1 <> 1 because R689C1 <= 22
f) ! Innies+Outies C1: -23 = R1C2 - R6789C1
-> R7C1 <> 2 since only combo R6789C1 = {2679} blocked by Killer pair (26) of 11(3) @ R3C1
g) 33(7) = 12567{39/48} -> R8C2 = 1, R9C3 = 2
h) 11(3) @ C3 = {146} locked for C3, 6 locked for N4
i) Innies+Outies N14: R6C3 = R7C2 = 3
j) 21(4) = 39{27/45} -> R6C1 = 9

5. R123
a) 15(2) = {78} -> R3C2 = 8, R4C2 = 7
b) Innies N1 = 13(3) = {148} locked for R3+N1
c) Hidden Single: R9C2 = 6 @ C2, R8C1 = 5
d) R7C1 = 4, R9C1 = 7 -> R9C4 = 8
e) Outies = 23(3) = {689} -> R8C4 = 6, R7C4 = 9

6. N568
a) 26(4) = {2789} because R7C56 = (257) -> R6C5 = 8, {27} locked for R7+N8
b) 3 locked in 25(6) @ N5 -> 25(6) = {123469}
c) 28(4) = 89{47/56} -> 8,9 locked for N6
d) R7C3 = 8, R8C3 = 9
e) Naked pair (34) locked in R8C56 for R8+N8
f) R8C9 = 2
g) 23(5) @ R5C7 = 567{14/23} -> 7 locked for N6
h) 28(4) = {5689} locked for N6
i) 23(5) @ R5C7 must have 5 and 6 and it's only possible @ R7C89 -> {56} locked for N9

7. N56
a) 23(5) @ R6C6 = {12578} -> R7C7 = 1, R6C6 = 5, R7C6 = 2
b) 16(4) = {2347} -> {247} locked for C4+N5
c) 25(6) = {123469} -> R2C5 = 4, R3C5 = 2
d) 23(5) @ R5C7 = {14567} -> 4 locked for N6, 1 locked for C8
e) R4C7 = 3 -> 28(5) = {23689} -> R2C8 = 2, R2C7 = 8, {69} locked for R3

8. Rest is singles.

Rating: 1.5. I used one forcing chain and a Hidden Killer quad.

[mhparker]

[sudokuEd]

[Afmob]

Great chain Ed! It's certainly simpler than mine. I rated ND 9 only "1.5" because when I solved it, it flowed quite well meaning I didn't really came to halt despite those difficult moves. Also my wt is quite short and doesn't have this many ! moves where as my other 1.75 walkthroughs are usually quite large and have many ! moves and they also wouldn't be cracked with one chain only.

My first version had combo analysis in R89 to remove some candidates from R7C1 (can't remember which ones) which I found quite complicated, so with it I would have surely rated ND 9 1.75. On the other hand, I immediately saw the chain which cracked the Killer. So maybe it's more a hard 1.5.

Compared to UA97 V2 which I'm tackling at the moment (made 4 placements so far) ND9 is way easier.

[mhparker]