(i just learned that Rec.Puzzles was a place where a mathematical result about Sudoku was first published. wow.)
https://www.youtube.com/watch?v=oPTe52OmMEk
Solve Diabolical Sudoku Puzzles - Very Hard
1,368,064 views
•Dec 20, 2016
(33 minutes !) -- i guess this Sudoku puzzle doesn't get (obvious and) easy until the very end... i think that's unusual.
--- in this video, this Wiz guy doesn't use any sophisticated methods... He just scans, and pencils in Candidates ONLY when they can be narrowed down to 2 possibilities.
(never 3)
my question is...
1. Are there Sudoku puzzles that are
so hard that humans can't solve them?
( what i mean is... )
2. Are there Sudoku puzzles that are
so hard that humans can solve them
only by simulating a Computer's exhaustive search ?
i.e. ... by doing backtracking
i.e. ... by doing a Look-Ahead of
(more than) 3 steps or so ?
HH
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