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GeneralRe: not guilty by reason of insanity Pin
dandy7219-Mar-18 5:13
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GeneralRe: not guilty by reason of insanity Pin
Pete O'Hanlon19-Mar-18 5:47
subeditorPete O'Hanlon19-Mar-18 5:47 
GeneralRe: not guilty by reason of insanity Pin
dandy7219-Mar-18 5:52
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GeneralRe: not guilty by reason of insanity Pin
shell78719-Mar-18 6:25
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GeneralRe: not guilty by reason of insanity Pin
Mycroft Holmes19-Mar-18 14:40
professionalMycroft Holmes19-Mar-18 14:40 
Generalsingularity's brink ? Pin
BillWoodruff19-Mar-18 0:07
mveBillWoodruff19-Mar-18 0:07 
GeneralRe: singularity's brink ? Pin
Marc Clifton19-Mar-18 1:24
mvaMarc Clifton19-Mar-18 1:24 
GeneralDifficult-to-solve Sudoku wanted Pin
Member 798912218-Mar-18 23:36
MemberMember 798912218-Mar-18 23:36 
I wrote a small (85 lines of C# code) backtraking Sudoku solver - primarily to illustrate the idea of backtracking. (After all, the fun of Sudoku is not "Press this button to se the solution", but exercizing your brain Smile | :) .)

Wikipedia claims that the general problem of solving a Sudoku "is known to be NP-complete". So I thought finding a Sudoku problem that could really stress a PC would be simple. Not true. The most difficult I have found until now solves in 3.4 milliseconds, evaluating about 110,000 tentative digit placements (about 30 ns per evaluation).

A typical "trait" of backtracking is that on the average it usually performs well, but the worst case performance may be bad. So I am searching for examples of that worst-case performance Smile | :) .

Where can I find Sudoku boards that are truly difficult to solve, even for a PC?

NP complete problems are extremely dependent on problem size, and 9 by 9 is not exactly a large problem. My solver can handle any board size, but I made a very quick and dirty user interface that handles 9 by 9 only, so I would like to stay within that size.
GeneralRe: Difficult-to-solve Sudoku wanted Pin
"mega"-in-a-fake-beard18-Mar-18 23:54
professional"mega"-in-a-fake-beard18-Mar-18 23:54 
GeneralRe: Difficult-to-solve Sudoku wanted Pin
User 742933818-Mar-18 23:58
professionalUser 742933818-Mar-18 23:58 
GeneralRe: Difficult-to-solve Sudoku wanted Pin
"mega"-in-a-fake-beard19-Mar-18 0:02
professional"mega"-in-a-fake-beard19-Mar-18 0:02 
GeneralRe: Difficult-to-solve Sudoku wanted Pin
OriginalGriff19-Mar-18 0:13
mveOriginalGriff19-Mar-18 0:13 
GeneralRe: Difficult-to-solve Sudoku wanted Pin
"mega"-in-a-fake-beard19-Mar-18 0:15
professional"mega"-in-a-fake-beard19-Mar-18 0:15 
GeneralRe: Difficult-to-solve Sudoku wanted Pin
Member 798912219-Mar-18 1:14
MemberMember 798912219-Mar-18 1:14 
GeneralRe: Difficult-to-solve Sudoku wanted Pin
F-ES Sitecore18-Mar-18 23:57
mveF-ES Sitecore18-Mar-18 23:57 
GeneralRe: Difficult-to-solve Sudoku wanted Pin
"mega"-in-a-fake-beard19-Mar-18 0:01
professional"mega"-in-a-fake-beard19-Mar-18 0:01 
GeneralRe: Difficult-to-solve Sudoku wanted Pin
Member 798912219-Mar-18 1:43
MemberMember 798912219-Mar-18 1:43 
GeneralSounding off on the responses Pin
W Balboos, GHB19-Mar-18 0:45
mveW Balboos, GHB19-Mar-18 0:45 
GeneralRe: Sounding off on the responses Pin
"mega"-in-a-fake-beard19-Mar-18 0:56
professional"mega"-in-a-fake-beard19-Mar-18 0:56 
GeneralRe: Sounding off on the responses Pin
W Balboos, GHB19-Mar-18 1:00
mveW Balboos, GHB19-Mar-18 1:00 
GeneralRe: Sounding off on the responses Pin
Jörgen Andersson19-Mar-18 2:05
professionalJörgen Andersson19-Mar-18 2:05 
GeneralRe: Sounding off on the responses Pin
Member 798912219-Mar-18 2:09
MemberMember 798912219-Mar-18 2:09 
GeneralRe: Sounding off on the responses Pin
W Balboos, GHB19-Mar-18 2:24
mveW Balboos, GHB19-Mar-18 2:24 
GeneralRe: Sounding off on the responses Pin
Jörgen Andersson19-Mar-18 2:30
professionalJörgen Andersson19-Mar-18 2:30 
GeneralRe: Sounding off on the responses Pin
Member 798912219-Mar-18 2:07
MemberMember 798912219-Mar-18 2:07 

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