Daily Puzzle, help
Am I?Posted: Wed Jan 9 2019 05:42 am

2019/01/04, 13x13 hard puzzle, can someone help me >-< ?

https://imgur.com/a/34UEHrN

Also, hi! I've been away for so long but the same people are still dominating the leaderboards o.o

I'll be away again soon since I'll be somewhere with really, really slow internet...I don't want anyone to see the +20 seconds my puzzles will get otherwise! 


morlPosted: Wed Jan 9 2019 06:07 am

Surface sums show that r5789c7 must be 17, this is only possible if r8c7 is 7 and r7c7 is not 4. I hope that helps. 


Am I?Posted: Wed Jan 9 2019 01:23 pm

I'm not sure what you mean by surface sums and why is r5789c7 = 17?


morlPosted: Wed Jan 9 2019 03:01 pm

In the lower left corner of this example, there are two "down" sums which add to 35, and three "across" sums which add to 31. The "down" sums involve an extra cell, in this case r4c2, which must be 35-31=4. The same thing is possible in the upper right corner as well. That gives r4c6=50-42=8. And it's possible in the 2018-01-04 puzzle, where the "across" sums are 38, 33, 29, 20 and 30 (rows 5, 7, 8, 9 and 10), and the "down" sums are 45, 28 and 21 (columns 5, 8 and 9).


Am I?Posted: Thu Jan 10 2019 12:21 am

Oh wow. I never thought to apply surface sums over such a big area. Thank you! 


AdminPosted: Thu Jan 10 2019 06:58 pm

Yes, surface sums are definitely used for the hard difficulty puzzles. They shouldn't be necessary for medium and easy, but they may speed up the process a bit.