Top products from r/sudoku

A bit late but might as well reply

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1. Look in the file archive of this group https://www.facebook.com/groups/309473799153072/?ref=bookmarks lots of great original sudoku puzzles are poster there. - Great thing about this website is that it shows the authors website so you get way more sources.
   
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2. The World Puzzle Federation Grand Prix Puzzles go back a few years - the sudoku is a great source for original variants https://gp.worldpuzzle.org/content/sudoku-gp
   
   Example: https://gp.worldpuzzle.org/sites/default/files/Sudoku%20Round1.pdf
   
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3. Gareth Moores website https://www.puzzlemix.com/puzzles.php is a great source for the "Standard" variants.
   
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4. Richards Puzzles on logic masters website is a great series: https://logic-masters.de/Raetselportal/Benutzer/eingestellt.php?name=Richard
   
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5. [Edit] Adding this http://sudokucup.com/content/daily-league (forgot about this website - needs registration)
   
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6. Physical books I highly recommend DJAPE puzzles and Gareths Moors (Mammoth Book of New Sudoku)
   
   - https://www.amazon.ca/Puzzles-Dr-Djape-300-puzzles/dp/1979609950/ref=sr_1_2?keywords=djape&qid=1558058506&s=gateway&sr=8-2
   
   - https://www.amazon.ca/Mammoth-Book-New-Sudoku/dp/0762449365/ref=sr_1_fkmrnull_1?keywords=mammoth+book+of+new+sudoku&qid=1558058540&s=gateway&sr=8-1-fkmrnull
   
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7. Youtube: "Cracking the Cryptic" - Youtube channel which solves a variety of sudoku puzzles (Note: Am Patreon)
   
   \^ They really like Sandwich Sudoku (outside clues), but it looks like they are exploring more variants recently.
   
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   Hope that helps - I need to save this as a common answer.
   
   Adding https://krazydad.com/ to the list

I've asked about the book here: Can anyone identify this book?

[edit: The OP answered that, giving the Amazon India reference. I found it on the U.S. site: Sudoku Puzzle Game Book Volume 1: 200 Puzzles by Chandra Singh. The US publication date is 2015, shipped by Amazon (which means they have it in stock), whereas the India listing has a 2016 publication date, and is from a books-on-demand publisher. It is entirely possible that the 2016 edition has been fixed. There are no comments in either place pointing out multiple solutions.]

And I also issued a challenge. I cracked this puzzle, but not the second. I had a conversation on Quora recently with a "puzzle personality" where he claimed that improper sudoku (those without a single and unique solution) were not "puzzles" because they cannot be solved. Well, it took me an hour, but I solved this puzzle, providing a pattern of numbers that satisfied the original and clear stated rules and then showing three more solutions (out of very many). Later, sudoku with multiple solutions were called "improper," which is a technical term. An improper sudoku is still a sudoku.

Ordinary methods will not do the trick, but Ariadne's Thread can, specifically the form recommended by Mepham in The Book of Sudoku 3 (2005) (which is Binary AT, with recursion). It can be done without guessing, just following a clear and reliable algorithm that will always work. I now think I could do it in about half that time. I will describe the technique in more detail on request. Very simple, very fast, far faster than people have claimed for AT.

To me, there is satisfaction in being able to solve any Sudoku, never being "stuck," knowing what to do to find solutions, developing process and making it efficient, and then, in explaining it such that at least one person gets it.

I personally get most my Sudokus online instead of books as I like variants more and there's more variety there. I have a few books that have satisfy my enjoyment of variants.

The Mammoth Book Of New Sudoku by Gareth Moore If you want a lot of puzzles, this will probably suit you well. It has many common and uncommon variants. This one also has some overlapping grid puzzles.

Sudoku Mix #1 by Logic Masters India: Classic Sudoku and 5 variants. Nice handcrafted puzzles. This one has a slowly increasing difficulty per variant. Good for beginning new variants.

Mutant Sudoku by Thomas Snyder and Wei-Hwa Huang A large number of puzzles per variant from easy to very hard. Some common and some uncommon variants. Very nice book, but does go outside the normal sudoku books a lot. I wish there were more books like this.

You can work up to it! I highly suggest getting this book
Mega Sudoku 16x16 Large Print - Easy - Volume 57 - 276 Logic Puzzles https://www.amazon.com/dp/1505649315/ref=cm_sw_r_cp_api_i_jemCDbW311WDS

Nick Snels makes awesome sudoku books and this is a large print edition which is very rare to find. You can start with easy or even get the easy to extreme one and work your way up!

Give him one of those:

Killer Sudoku ultrahardcore

Sudoku - Intuition schlägt Logik

They are both from a German publisher, but hopefully available in other countries as well. These puzzles are usually very hard and most require AIC/ALS-type techniques to solve.

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Edit: Give him these for now and see how fast he can solve them:

...........38..1.5.7..12.6.6....39...5..8..2...75....4.1.95..4.2.9..45...........
.2...4.978.....1....762.....56.4.8.............9.6.34.....732....5.....337.8...6.
6....8.24.....7..1.5.4..9...189....5.........7....541...9..3.6.5..7.....14.2....3
79.....2....7...8...85124..23.........4.6.2.........41..93487...2...9....7.....94
..9.5..7...83.4...26...7.1.627..........8..........457.7.9...63...1.67...4..7.9..

Check out this one, I do sudoku all the time and I found it very challenging.

https://www.amazon.com/Power-Player-Games-Hard-Sudoku/dp/1698858434

Amazon has it.