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annette
New kid on the Grid

Joined: 29 Sep 2006
Posts: 1

 Posted: Fri Sep 29, 2006 11:29 pm    Post subject: nš18 Loved it helped me to forget my flu. toook me almost 2 hours though.
sudokuEd
Grandmaster

Joined: 19 Jun 2006
Posts: 257
Location: Sydney Australia

Posted: Fri Oct 06, 2006 9:02 am    Post subject: Re: nš18

 annette wrote: Loved it

Me too.
 Ruud wrote: It takes a lot of nibbling before you are able to place the first digit. Halfway there is another obstacle to remove. This is a true Assassin. Enjoy!

I was greedy and got straight into the Mains - then got indigestion halfway through!

1. "45" on N9 -> 2 outies = 13 -> no 1, 2 or 3 in r6c8 or r8c6

2. "45" on N7 -> 2 outies = 7 -> no 7, 8 or 9 in r6c2 or r8c4

3. "45" on r789 -> 2 outies = 13 -> r6c28 = [67/58/49]

4. "45" on N8 -> 2 innies = 7 -> r8c46 = [16/25/34]

5. from step 3. r6c8 = {789}. "45" on N36 -> 3 innies = 12 -> r6c8 + r56c7 (with no 1 in r6c7) = [912/813/714/7{23}] -> r5c7 = {123}, r5c6 = {456}, r6c7 = {234}, r6c6 = {789}

6. Another way of expressing the information from step 5 is that r6c678 = [929/838/747/927/837]. Clearly, several of these have a problem! -> r6c8 = 7, r6c67 = [92/83] -> r6c6 = {89}, 2 innies of N36 now = 5 = {23} -> naked pair on {23} in c7 and N6 -> no 2 or 3 elsewhere in these. r5c6 = {45}

7.r8c46 = [16] (step 1, 4), r6c2 = 6 (step 3)

8. r5c34 = 16 = {79} -> no 7 or 9 elsewhere in r5 -> r5c34 = [97] (hidden single 7 in N5)

9. 21 (4) cage in N6 now {1569} only since 2,3 and 7 are blocked, with 9 only in c9 -> no 1,5,6 or 9 elsewhere in N6 and no 9 elsewhere in c9

10. r4c78 = {48} -> no 4 or 8 elsewhere in r4 or 20(4) cage in N36

11. "45" on N5 -> 2 outies = 1 innie. Since r56c7 = {23} = 5 -> r6c4 = 5, r6c3 = 4, r5c67 = [43], r6c67 = [92], r56c5 = 11 = [83], r6c19 = [81], r5c89 = {56} pair = 11 -> r4c9 = 9, r5c12 = {12} pair in N4 = 3 ->r4c1 = 5

12. r4c23 = {37} pair = 10 -> r3c23 = 5 = [41] (not {32} since {37} pair in same cage)

13. r4c78 = {48} = 12 -> r3c78 = 8 = [53/62]

14. 31(5) cage in N698 now = 18(3) = {189/459} = 9{18/45} = [5/8..] -> no 9 elsewhere in N9

15. 18(4) cage in N9 = {2367/2457/3456} (not {2358} blocked see step 14) -> no 8 in 18(4) cage

16. 8 in c9 now locked in N3 -> no 8 elsewhere in N3 (including r1c8)

17. "45" on r 9 -> 2 innies = 9 -> no 1 or 9 in r9c1, no 4 in r9c9

18. 25(5) cage in N478 now 18(3) cage = {279/378} = 7{29/38} -> no 5. No 7 elsewhere in N7 -> 7 in c1 locked in N1 in 24(4) cage -> no 7 elsewhere in N1 (including r1c2)

19. "45" on c9 -> 3 outies = 14. r5c8 = {56} -> r19c8 = 8/9. Min r8c8 = 2 -> max. r1c8 = 7 -> no 9 in r1c8

20. 9 in N3 locked in 17(3) cage = 9{17/26/35} -> no 4

21. 4 and 8(step 16) in N3 now locked in 20(4) cage = 4+8=12 -> other 2 cells= 8 = {17/26/35}

22. "45" on c1 -> 3 outies = 15. r5c2 = {12} -> r18c2 = 13/14= {58/59} = 5{8/9} -> no 5 elsewhere in c2 and no 2 or 3 in r18c2

23. r9c23 = 7 = [16/25] -> r9c2 = {12} -> naked pair on {12} with r5c2 -> no 1 or 2 elsewhere in c2

24. 4 in N7 locked in 20(4) cage = 4{169/259} (not{268} since [2/6] needed in 7(2) cage in N7 - (not {3458} since 5 and 8 in 20(4) cage both only in r8c2) -> 20(4) cage = 49{16/25} -> no 9 elsewhere in N7 and no 3 or 8 in 20(4) cage

25. 3 and 8 in N7 now locked in 18(3) cage = {378} only

26. 3 in c1 now only in N1 in 24(4) cage -> no 3 elsewhere in N1

27. 16(3) cage in N1 = {259/268} = 2{59/68} -> no 2 elsewhere in N1

28. naked triple on {589} in r128c2 -> no 8 in r7c2 -> 8 locked in r78c3 for c3 & r2c12 for N1

29. from step 24, the {1469} combination in the 20(4) cage in N7 is the only combination (in the 20(4) cage) that uses 1 or 6 with the 1 only available in r7c1 -> 6 must be in r9c1 in this combination -> no 6 in r7c1 ->r7c9 = 6 (hidden single r7), r5c89 = [65]

30. rest of 18(4) cage in N9 now 12(3) cage = {237/345} = 3{27/45} -> no 3 elsewhere in N9

31. "45" on c9 -> 2 outies = 8 -> r18c8 = {35} pair -> no 3 or 5 elsewhere in c8 -> r3c78 = 8 =[62]

32. 20(4) cage in N3 now {3458} with r1c8 = 5 and no 7.
the rest is basically hidden and naked singles

[1Nov-edited - especially inaccuracies in step 24 - thanks Andrew. 3Nov-edited:clarity for step 29:typo step 31]
Oscar
Regular

Joined: 16 Jan 2008
Posts: 28
Location: Montesson

 Posted: Sat Mar 01, 2008 3:25 pm    Post subject: SudokuEd Walk Through is really very good. I did some swinging from innies at N4-N8 and N6, but did not identify the link to close the cycle between N6 and N4! Central rows, R456 get quickly done and then up & down, from R123 <-> R789, digit by digit. I did turn my back to this one and had to restart a couple of times Arround 3 hours solving time I would rate it 1.25_________________Nothing can both be and not be
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