[Community Puzzle] 25x25 Sudoku

Puzzles
21

DlxSolver does select the most constrained column by design, yes

22

Hi, sorry for asking, but how much complicated is it to solve the problem without backtracking ?
I could solve the first test in 8 steps with a simple algorithm (6 steps now), but even with some more advanced tricks Iā€™m not confident anymore I can do other tests without brute force.

Are such sudoku problems doable without *any* backtracking ?

Thanks :slight_smile:

23

Same here. I can solve the first test case without backtracking. After that, it gets a lot harder. I found some techniques online that I havenā€™t had a chance to implement yet, so maybe ā€¦ someday.

1 Like
24

I solve all the grids using the following algorithm (loop):

  1. There is only one possible letter left for a cell.
  2. In a group of cells (row, column, block), a letter is present only once.
  3. In a group, n cells have only n possible letters (so we eliminate these letters from the other cells).
  4. Make a hypothesis in the cell with the fewest possible letters.

With this algorithm, I solve all the grids with a maximum hypothesis depth of 25.

I coded it in JavaScript; there are no timeouts.

25

I finally made it in python using Timinatorā€™s DLX algorithm, however I find it odd how the execution time spansā€¦ When running the 5th test case, I get times in a [900,5800+] ms range