Sudoku Solver in Common Lisp (2009) 33 points by deepaksurti 25 days ago | hide | past | web | favorite | 12 comments

 I had a go at solving sudokos, but I found the experience tedious, mechanical and far too easy to make a mistake.In fact just the frustration inducing thing to tickle the first of the virtues of a programmer: "Laziness". I then wrote a solver in Python which was far more fun than solving sudokus by hand and has the advantage that I never need to solve one of the dratted puzzles again ;-)I recommend it as an exercise for all programmers!I didn't document that process, but I did for solving a different puzzle which you may enjoy if you need inspiration: https://www.craig-wood.com/nick/articles/snake-puzzle/
 I enjoy solving Sudoku puzzles. I had a puzzle book that I solve everyday on commute to school.Then I created a solver in Python as well, it uses backtracking. It can solve the puzzle instantly. Never solved another sudoku puzzle ever since.
 I wrote a program that generates all sudokus that satisfy constraints given in a partially filled grid. I thought it might be feasible to find out the distribution of 81 digit numbers that are valid Sudokus by such brute force. Since there are so many sudokus, I made the program capable of resuming an interrupted computation using a dump file. All this I did in C. It was quite a learning experience. Here goes: (https://github.com/vyuh/sud.c)For some fun I also translated the algorithm to Javascript (https://github.com/vyuh/sud.js) and Java (https://github.com/vyuh/sudoku-lister/blob/master/java/sudok...). The javascript code is used in a toy browser application i made (https://su-do-ku.herokuapp.com/).Some day I might generalize the program to larger Latin Squares (https://en.wikipedia.org/wiki/Latin_square).
 If you found this interesting, see also Norvig's Sudoku Solver [1], with an implementation in Python.
 I enjoy these puzzles a lot in my commute time. Recently on a flight to Germany I built a solver in python. It was a pretty great way to consume a portion of the long flight from US.I’ve recently started reading up on optimization strategies, my first attempt was pretty straightforward. It’s a fun exercise I recommend for anyone who likes solving these puzzles manually.
 If you haven't already seen it, check out Donald Knuth's Dancing Links algorithm for solving sudoku. Here's a good overview and intro (that includes a link to the paper).
 If anyone is interested in these kind of coding challenges, there are a few Sudoku solver puzzles on Codewars: https://www.codewars.com/kata/search/?q=sudoku
 I wrote a sudoku solver in Visual Basic 5 many years ago. I've lost the source code to it but I remember the algorithm mostly. I've been meaning to re-implement it in a new language as a learning/practice exercise.
 Damn near impossible to read the code in those blockquote blocks :(
 A more readable version on github. [1]
 The author doesn't understand what blockquotes are for I think.
 One could also write a sudoku solver in z3. I did this for an assignment and it was fun. I have never programmed in Lisp before but there seems to be some similarity between them.

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