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multiple solutions to 1Oct14, 4x4 Difficult? https://www.calcudoku.org/forum/viewtopic.php?f=18&t=625 
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Author:  Rob [ Wed Oct 01, 2014 2:31 am ] 
Post subject:  multiple solutions to 1Oct14, 4x4 Difficult? 
It appears to me that there are multiple solutions to the 4x4 difficult puzzle today. Here is what I have so far: It appears to me that the first row can be either 3412 or 4312 equally correctly. 
Author:  apolaris [ Wed Oct 01, 2014 2:56 am ] 
Post subject:  Re: multiple solutions to 1Oct14, 4x4 Difficult? 
I found a similar problem: 4 3 1 2 3 4 2 1 2 1 4 3 1 2 3 4 and 4 3 1 2 3 4 2 1 1 2 4 3 2 1 3 4 are both equally valid solutions, yet both are being rejected as "incorrect" when submitted. 3 4 1 2 4 2 3 1 2 1 4 3 1 3 2 4 is being accepted as the solution, but it's nowhere near being the only one. 
Author:  bram [ Wed Oct 01, 2014 4:12 am ] 
Post subject:  Re: multiple solutions to 1Oct14, 4x4 Difficult? 
Apart from four correct solutions with this arrangement of numbers in the right half of the puzzle: x x 1 2 x x 2 1 x x 4 3 x x 3 4 there is also this (fifth) correct solution: 3 4 1 2 4 2 3 1 2 1 4 3 1 3 2 4 On my system (latest Firefox version on Windows Vista SP2) all five solutions are accepted as correct when submitted. 
Author:  calcpnm [ Wed Oct 01, 2014 9:16 am ] 
Post subject:  Re: multiple solutions to 1Oct14, 4x4 Difficult? 
Thanks for letting me know. I'm as far as having figured out that this is a bug introduced in a more recent version of my solver I ran an old version of the solver (from July 2010 (!)) on this puzzle, and it found all five solutions. Edit: found the bug, a fix for a problem which caused it to not be able to solve puzzles larger than 15x15 (which I needed for the new book, which has one 17x17 puzzle) introduced a new bug for puzzles with cages larger than 5 cells Challenge to you all: how to modify the current puzzle so only this solution: Code: 3 4 1 2 4 2 3 1 2 1 4 3 1 3 2 4 is valid?? Edit #2: I changed the puzzle a bit so the above is a single valid solution. Patrick 
Author:  clm [ Wed Oct 01, 2014 10:30 am ] 
Post subject:  Re: multiple solutions to 1Oct14, 4x4 Difficult? 
calcpnm wrote: ... I'm as far as having figured out that this is a bug introduced in a more recent version of my solver I ran an old version of the solver (from July 2010 (!)) on this puzzle, and it found all five solutions. ... Patrick It was one possibility among 5, but I was so unlucky that only when I entered the fifth I got the 2 points . I was really surprised since it was the first time (IIRC) that I was seeing a violation of the "dogma" of the unicity, and thinking what would have happened in case of a 9x9, ... . I supposed most players were going to feel the same and find the solution given as correct by the program in a couple of minutes (the other four times the full grid was green but the program insisted in an "incorrect solution") and I was waiting until 24.00 CET today to talk about this bug (this time only 2 points, anyway ). 
Author:  pnm [ Wed Oct 01, 2014 10:44 am ] 
Post subject:  Re: multiple solutions to 1Oct14, 4x4 Difficult? 
clm wrote: I supposed most players were going to feel the same and find the solution given as correct by the program in a couple of minutes Yes, and every time this happens (a validated solution is submitted but rejected by the server) I get a warning message, to alert me of a potential bug. So this morning I had 400+ emails in my inbox Edit: and after exhaustively testing all October puzzles, I found that I have to replace five more 4x4 difficult puzzles (which had 3 or 5 solutions) 
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