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# Tough Sudoku for 12/January/2011

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 SE=7.2 12/Jan/11 12:10 AM Lovely! I love visiting gardens in different areas. 12/Jan/11 12:10 AM Beautiful setting, Anne! 12/Jan/11 12:22 AM Oh! I love to see and hear a waterfall! Thanks! Have a great day everyone! 12/Jan/11 12:34 AM 1. Note f45=48.Unique possibilities to 26.2. If b5=9,gh5=47,d5=1,c5=5,ac4=38;h4 has no candidate.So b5=1.UP46.3. If g1=9,g5=7,i9=8(i2=8,g2=3 would allow an unresolvable 167 rectangle at cei13);17 have no place in row 9.So g5=9.UP81. 12/Jan/11 1:19 AM Isn't this in the middle of wine-tasting country? Beautiful gardens ... good wine ... what's not to like?! 12/Jan/11 1:38 AM solves neatly w/o invoking uniqueness usind als chains:1.(137=9)a6b56-(9=347)h45g5 => ac4<>3,c5<>7 UP=482.(7=349)h45i4-(9=167)cei1-(1)h1=h78-(1=378)cgi9 => h17<>7 UP=81 12/Jan/11 1:40 AM note: Apr-26-09 SE=8.3, another super easy 8.x puzzles that the solvers almost but didn't nail - 1 depth 3 AIC. 12/Jan/11 2:23 AM In comments above, After UP=26, Alfred uses 12 cells in his solution; farpointer uses 20. Guess which one is most efficient. 12/Jan/11 3:42 AM similar to farpointer's.1. SST to UP=26.2. (1)f6=(1-5)d5=c5-c4=(3489)acfh4-(9)i4=g5-(9=1)b5 => d5<>1UP=48.3. (7=4)h5-(4=3)h4-(3=9)i4-i1=(9-2)g1=(2-1)h1=h78-i9=(1-7)d9=hi9 => h17<>7UP=81. 12/Jan/11 4:28 AM Oh dear. My convoluted path to the solution followed the approximate UP sequence 26-27-29-47-49-81, so I dare not repeat it here :-) I don't see why we couldn't have separate 'awards' for the most efficient solutions with and without using unique rectangles. Or any other way of defining a More... 12/Jan/11 5:05 AM note: just posted solution for unsolved Apr-29-09 SE=7.7 tough. Remarkably this one starts at given of 22 and no eliminations or UPs of any sort. Nevertheless, a swordfish and two short AICs solve the puzzle nicely. Alfred nuked the puzzle that day with a depth 15+ forcing net and other solvers More... 12/Jan/11 5:15 AM Neil: I have already conceded that the only thing more efficient - but perhaps not more mindless - than using a forcing net, is to feed the puzzle to software which brute forces the final position. 12/Jan/11 5:46 AM note: as a chess player, I have grown to distrust long variations, for they almost always contain errors of omission. They are also, in my experience, unnecessary - one only need look a few short moves ahead, provided one understands the position. 12/Jan/11 6:09 AM For step 1 also:1)(5=hp56)cdi4-(9)i4=g5-(9=1)b5-(1=5)d5,=>d4c5<>5.UP=48 12/Jan/11 6:22 AM Optimized solution.#0. SSTS -> UP26#1. 9i4=9g5-(9=1)b5-(1=5)d5-(5=6)d4 : -6i4; UP48#2. 7h5=7g5-9g5=9g1-2g1=2h1*-1h1=1h78-1i9=1d9-7d9=7gi9**: *-7h1,-7h7; UP48Total of native SIS : 10 (3 cells and 7 strenghts in location) 12/Jan/11 6:30 AM Sorry for typos. Edit again : Optimized solution.#0. SSTS -> UP26#1. 9i4=9g5-(9=1)b5-(1=5)d5-[(5=6)d4 AND 5f6=5i6] : -56i4; UP48#2. 7h5=7g5-9g5=9g1-2g1=2h1*-1h1=1h78-1i9=1d9-7d9=7gi9**: *-7h1,-7h7; UP48Total of native SIS : 11 (3 cells and 8 strengths in location) 12/Jan/11 6:37 AM Brrrr ... Sorry for typos. Edit again : Optimized solution.#0. SSTS -> UP26#1. 9i4=9g5-(9=1)b5-(1=5)d5-[(5=6)d4 AND 5f6=5i6] : -56i4; UP48#2. 7h5=7g5-9g5=9g1-2g1=2h1*-1h1=1h78-1i9=1d9-7d9=7gi9**: *-7h1,**-7h7; UP48Total of native SIS : 11 (3 cells and 8 strengths in location) 12/Jan/11 6:39 AM OMG !! Finally : read #2. ...; UP81 ! 12/Jan/11 7:19 AM farpointer must be reminiscing from his chess playing in primary school. In top competitive chess, the deeper the combination, the higher it is regarded. Beginners cannot see as far ahead as masters, and would not be expected to pull off a long combination.For a given Sudoku puzzle,the shortest More... 12/Jan/11 9:14 AM Hehehe! I actually ercognisde that as it came up! 12/Jan/11 1:38 PM I mean recognised! Serious finger fumbles today! 12/Jan/11 1:38 PM The gardens are much greener in that pic than we were last there. Great to see! 12/Jan/11 2:29 PM Alfred makes a good point in his post above ("the deeper the chain... the more difficult...") re sudoku puzzles. Also, farpointer has sometimes questioned the SE ratings, where a slightly longer chain solution gives a high SE rating (eg, 8.n), and a few (or more than a few) of More... 12/Jan/11 11:31 PM define "chain" Neil. 13/Jan/11 3:56 AM