Sudoku: how to?
> A fiver says you don't simply try every possible permutation of digits in each box until you get to the right answer – the number of Sudoku solution grids has been calculated as 6,670,903,752,021,072,936,960. No, you apply logic and deduction to identify which numbers go where, and it takes just a few minutes to solve the puzzle.
Strictly speaking having that many solution grids doesn't relate to the complexity of solving any given puzzle, it's the reason you don't attempt to store all the possible puzzles and do straightforward lookup.
...Perhaps pedantically (humour me, from here on in I'm addressing fellow puzzle fanatics and not the direction of the article), hoping to find it obvious "where the numbers go" throughout doesn't suffice technically either; only when you have in effect determined a search tree, pruned it until [relatively] sparse, and then walked it can you argue you have properly iterated and eliminated all impossible situations (thereby including "where the number's *don't* go") as per Occam's razor at every step from start to finish.
One solution -and only one- always results for me for solving by hand, as required. I've written some of my methods as code, but not all ... however at this point I am suspicious of the possibility that typical "brute force" solvers may be at risk of (mis)identifying a puzzle as having multiple solutions when it's not necessarily the case...