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Str8ts Weekly Extreme #49 - Solution

Solution to the weekly extreme Str8ts puzzle #49 from www.str8ts.com

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Str8ts Weekly Extreme #49 - Solution

  1. 1. Weekly Extreme Str8ts Puzzle #49 May 29 – June 4, 2011www.str8ts.com<br />Solution bySlowThinker<br />
  2. 2. Start position<br />Extreme Str8ts #49 cannot be solved without testing/guessing. A possible reason is that there are very few small compartments.<br />Solving<br />A5=8c<br />A7=7c<br />G1=7c<br />
  3. 3. Solving…<br />J1=4p<br />H9=7s<br />B4=7s<br />D7=3s<br />Note: after J1=4, A3=26 which is a large gap pair, that removes 26 from A12.<br />
  4. 4. Testing GH2=89<br />Using conventional methods and rules we are stuck at this position. As you can see, there are only a few fields with two candidates. And even if you test one of those fields, you cannot draw easy conclusions.<br />An interesting candidate is 8, due to Setti’s rule. GH2 also intersects with 3 in row H, which in turn influences C8. This is why I tested GH2=89 first.<br />
  5. 5. Testing GH2=89<br />G2=8g, H2=9g  H8=3s, C8=8  B8=9c<br />On the other hand, due to Setti’s rule on 8: D3=8S8<br /> F3=6, A3=2, H3=1<br /> B3=9<br />Which produces a contradiction.<br />Therefore,GH2 cannot be 89. <br />
  6. 6. Testing D3=8<br />If we test 8 with Setti’s rule, we see that only column 2 and row D are undecided.<br />As row D contains only a single 8, let’s test D3=8, which forces an 8 in column 2.<br />
  7. 7. Testing D3=8<br />D3=8 removes 2 from D56 (yellow).<br />On the other hand:<br />D3=8  CE2=78S8  C3=7s  C2=8  C8=3  H8:-3  H2=3s  G2=2c  2 is removed from G567 (yellow)<br />That only leaves E5 and E6 for the 2s in columns 5 and 6 (red)  an illegal position.<br />Therefore D3 cannot be 8 and column 2 doesn’t contain an 8 either(Setti on 8).<br />
  8. 8. Solving…<br />H8=3s<br />C8=8<br />B8=9c<br />F3=8s<br />G4=8s<br />E7=8s<br />
  9. 9. Solving…<br />J7=9<br />J9=8<br />H7=5s<br />
  10. 10. Optional:checkingrow D<br />Row D must contain a 7.<br />There are two ways to detect this:<br />There’s a 7 in every column, therefore (according to Setti’s rule) there must be a 7 in every row.<br />The swordfish on 7 at CDE236 is “built” using columns, and thus forces a 7 in each of its rows as well.<br />(This step is optional and not necessary, in order to solve the puzzle.)<br />
  11. 11. Setti on 9<br />Checking Setti’s rule on 9 we find that all but row D and F contain a 9. Columns 1 and 2 do not contain a 9 either, so columns 4 and 9 must contain a 9.<br /> H4=9S9<br />
  12. 12. Solving…<br />C3=9s<br />D3=7s<br />D6=2<br />D5=6<br />J5=5<br />J4=6<br />F4=5<br />
  13. 13. Solving…<br />C5=1<br />G8=5p<br />G6=4<br />E6=7<br />C6=5<br />
  14. 14. Solving…<br />A2=3p<br />A3=2c<br />A1=4c<br />C2=7p<br />H3=1<br />H2=2<br />G2=1<br />
  15. 15. Solving…<br />B3=6<br />B2=4<br />B9=5<br />E2=6<br />E8=4<br />F8=6<br />F7=4<br />
  16. 16. Solving…<br />C7=6<br />C1=3<br />C9=4<br />G7=2<br />B7=1<br />B1=2<br />E1=1<br />
  17. 17. Solving…<br />E9=9<br />E5=2<br />G5=9<br />G9=6<br />
  18. 18. Done<br />This puzzle shows how important small compartments are for removing candidates.<br />With many large compartments and small compartments at the fringe, it is not easy to solve the puzzle.<br />
  19. 19. Glossary<br />Letters appended to steps indicate the last strategy used, just before filling in a field:<br />No letter … number was last candidate in field<br />s … single (last) candidate for that number in compartment<br />c … compartment range check<br />d … stranded (unreachable/impossible) digits removed<br />h … high/low range check across compartments<br />p/t/q … naked pair / naked triple / naked quadruple<br />ph/th/qh … hidden pair / hidden triple / hidden quadruple<br />x … X-wing (2 rows / 2 columns)<br />w … Swordfish (3 rows / 3 columns)<br />j … Jellyfish (4 rows / 4 columns)<br />L … large gap field<br />Sx … Setti’s rule (count the numbers rule) – ‘x’ is the analysed number<br />u … unique rectangle<br />y … Y-Wing or XY-chains<br />
  20. 20. Weekly Extreme Str8ts Puzzle #49www.str8ts.com<br />Solution by SlowThinker<br />Note: there are other (maybe easier) ways to solve this puzzle.<br />

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Solution to the weekly extreme Str8ts puzzle #49 from www.str8ts.com

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