20150513, 02:46  #1 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
22255_{8} Posts 
An autoeroica sudoku
The hardest sudoku I ever solved.
I had to go twice (after solving it in 1hr); only on the second pass, I found some smart moves. 
20150513, 03:53  #2 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
41×229 Posts 
Granted, the old sudokus in the other threads are even harder.
The difficulty rating sites all happen to be blocked from work. Will check it from home, later. 
20150513, 12:01  #3 
Account Deleted
"Tim Sorbera"
Aug 2006
San Antonio, TX USA
4267_{10} Posts 
I entered it into this Sudoku Solver site.
The toughest part of the puzzle can be solved with what they call "simple colouring" (rule 4) ([URL="http://www.sudokuwiki.org/Singles_Chains"]link[/URL]) Last fiddled with by MiniGeek on 20150513 at 12:08 
20150515, 15:20  #4 
Romulan Interpreter
Jun 2011
Thailand
3^{3}×347 Posts 

20150515, 19:28  #5  
1976 Toyota Corona years forever!
"Wayne"
Nov 2006
Saskatchewan, Canada
4601_{10} Posts 
Quote:
http://www.mersenneforum.org/showpos...13&postcount=5 If you can solve it be hand you could tell the developers of the solver above what techniques they are missing. Last fiddled with by petrw1 on 20150515 at 19:29 

20150515, 22:58  #6  
Account Deleted
"Tim Sorbera"
Aug 2006
San Antonio, TX USA
17·251 Posts 
Quote:
If my own experience means anything, if you solve a puzzle that hard by hand without resorting to trialanderror, it's because you made a mistake somewhere and thought you could definitively eliminate one or more options that were actually still open. If you wanted to take a serious byhand stab at it, record your steps one way or another (paper writing down moves, camera recording what you do, or what have you) so you can follow along later with the help of a tool to see if you did it right. Last fiddled with by MiniGeek on 20150515 at 23:04 

20150515, 23:44  #7 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
9389_{10} Posts 
"Woah!!" vs "Very hard" (...vs newspapergrade "veryhard" which are easy)
There are some escratchpadtype Sudoku helpers. I run one of these, to save paper. It has unlimited undo, and the equivalent of small digit marking as well as save/read from savefile; it has (weak) hints, too, which I don't use. And it rates and generates random ones (also 16x16 and/or killers). It is called Sudoku Tiger (by one Adam A. Brown) but I don't remember where I got it from, it's been a long time ago; I searched for it again, and it wasn't easily found. Of course, it won't correct you if you simply guessed luckily (it doesn't know what is on your mind  maybe you spent some time thinking and doodling on a throwaway piece of paper); it only slaps you if you guessed unluckily. I've sometimes used it to go back and figure out if I cut corners inadvertently (which is equally as bad).
It rates the one with which I started as "Very hard" (but it is a very broad definition; some of its "Very hard" are like that one, and others, quite easy). Needless to say, when I entered the monster combination, it rated it "Woah!!" (no kidding, that's what it did). 
20150516, 00:15  #8 
1976 Toyota Corona years forever!
"Wayne"
Nov 2006
Saskatchewan, Canada
10771_{8} Posts 
Yes, I understood that....so now I am asking him if he can solve the Extreme one by hand......

20150516, 08:07  #9  
Romulan Interpreter
Jun 2011
Thailand
3^{3}×347 Posts 
Quote:
I didn't try the one from the other thread, but hey, there is a weekend tomorrow... Usually I play with "daily sudoku", an android app from enjoysudoku.com (must see!). It has lots of levels, the hardest being "diabolical", "nightmare", and "maelstrom". I generally play in the second half, up to forth quarter of the list sorted in increased order of difficulty, I almost always use autopencil marks, and almost never take a hint. In fact, I don't like the hints offered by that program, and that is the only thing I don't like about it. This is because they make a heavy use of "unique rectangle rule" (i.e. "if this cell would be 3, then the game would accept a double solution, so 3 can be excluded). The "unique rectangle" is a very debated rule in the sudoku world, usually you don't need it, and those numbers should be eliminated by other rules, more or less complicate. Every time when I hit a UR posibility, I play the "forbidden" variant (the "3" in the example above), and if indeed it is a game which may accept a double solution I close it immediately, uninstall/delete the program completely, and look for something else. Yes, all the games should (MUST) have unique solution, but you must NOT use this in solving the games. You can read more in sudokupedia, or around, there is an endless debate about it. About "telling to the developers of the solver above what techniques they are missing", they are not missing any technique. All "techniques" are just fancy names for shorter or longer coloring chains, and a bit of backtracking. For example, a hidden pair (and a pair in general) is a chain of length 2. A "xwing", is the same chain of length 2, which is spreaded over a larger area, eventually between different biscuits (a biscuit is one of the 3 areas of 3x9, horizontal or vertical, including 3 squares that touch laterally in a single direction). If you switch biscuits, or switch rows/columns in the same biscuit, the difficulty of the game stays the same. In the solving sites you mention, they are not "missing" procedures, for example you can click "count solutions" and it may tell you if the grid has a unique solution or not, this mean they can solve it. A little backtracking does wonders. The daily sudoku I am talking about has "auto coloring" if you want to use it, and I am sometimes using it for very complicate games. The game maintains tops for different conditions, like "you are faster than 81% of the people in the world who solved this grid using autopencil marks, without using auto coloring and with taking no more than 2 hints" (for example). The version of the game which is free will give you a single grid per day per level, but don't be upset about, there are enough levels, and for some of those grids you can work hours... Last fiddled with by LaurV on 20150516 at 08:31 Reason: tpyos, hnudreds of tehm 

20150516, 15:49  #10  
"Mike"
Aug 2002
2^{2}·2,011 Posts 
Quote:


20150516, 15:58  #11  
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
22255_{8} Posts 
One must wonder how hard is the "Cancel" category!
Quote:


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