An auto-eroica 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.

Granted, the [URL="http://www.mersenneforum.org/showpost.php?p=160113&postcount=5"]old sudokus in the other threads[/URL] are even harder.
The difficulty rating sites all happen to be blocked from work. Will check it from home, later.

I entered it into this [URL="http://www.sudokuwiki.org/sudoku.htm?bd=......1..5.6...3...9...7...1.....5.9...76....7..5...2...3..2.6....31....4.7......"]Sudoku Solver[/URL] site.

[SPOILER]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])[/SPOILER]

[QUOTE=Batalov;402225]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.[/QUOTE]
Solved on paper in less then 25 minutes.
(I consider myself a very strong sudoku solver)

[QUOTE=LaurV;402349]Solved on paper in less then 25 minutes.
(I consider myself a very strong sudoku solver)[/QUOTE]

This one????

[url]http://www.mersenneforum.org/showpost.php?p=160113&postcount=5[/url]

If you can solve it be hand you could tell the developers of the solver above what techniques they are missing.

[QUOTE=petrw1;402364]This one????

[url]http://www.mersenneforum.org/showpost.php?p=160113&postcount=5[/url]

If you can solve it be hand you could tell the developers of the solver above what techniques they are missing.[/QUOTE](he said he solved the rather-difficult one in this thread, not the extremely-difficult one in the other thread, in case that wasn't too clear...there are two different active sudoku threads right now)

If my own experience means anything, if you solve a puzzle [I]that[/I] hard by hand without resorting to trial-and-error, 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 by-hand 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.

"Woah!!" vs "Very hard" (...vs newspaper-grade "very-hard" which are easy)
 

There are some e-scratchpad-type 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 throw-away 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).

[QUOTE=Mini-Geek;402373](he said he solved the rather-difficult one in this thread, not the extremely-difficult one in the other thread, in case that wasn't too clear...there are two different active sudoku threads right now)

.[/QUOTE]

Yes, I understood that....so now I am asking him if he can solve the Extreme one by hand......

[QUOTE=petrw1;402380]Yes, I understood that....so now I am asking him if he can solve the Extreme one by hand......[/QUOTE]
Yes, I solved the one posted by Serge and I wanted to show my muscles because I solved it in half of his time. :flex::showoff:

I didn't try the one from the other thread, but hey, there is a weekend tomorrow... :razz:

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 [U]almost always[/U] use auto-pencil 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 "x-wing", 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 [U]single[/U] 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...

[QUOTE=LaurV;402404]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).[/QUOTE]We use the same app on iOS. We can usually solve the "intricate" puzzles. We also use auto-pencilmarks. On the easier levels the auto-pencilmarks solve the puzzle! We are at the point that we can solve most "ordinary" sudoku books. (The ones that are at the dollar store. The puzzles are usually rated from one to four stars.) We really need to improve but we are trying to teach ourselves without outside assistance.

:mike:

One must wonder how hard is the "Cancel" category! :buddy:
[QUOTE]Cancel my subscription to the Resurrection
Send my credentials to the House of Detention
I got some friends inside [/QUOTE]