C++ Sudoku Solver in 7 minutes using Recursive Backtracking

C++ implementation of a Sudoku solver.

We use a recursive backtracking algorithm and the bitset data structure.

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[Bananaa]

This was very close to a Java programming assignment at my university, going back and looking at the problem again feels refreshing. At the time I remember looking at some bit operations that had optimised peoples algorithms quite heavily and I brushed it off as too complicated for me at the time haha.

Really helpful video.

[gravysnake]

you know there a good programmer when you can see eyebags

[luziferius]

“Slap that like button an odd number of times.”. Nice! 😂

[WysockiD]

This channel is about to 10x, grateful to have found you early. youtube algo is on your side, ride this momentum and pump out the quality content, all the best man.

[nicke]

Took me 2 min to realize I wasn't looking at Python and was wondering why none it looked right to me..

[vorpal]

For a much more efficient (but programmer time consuming) approach to solving Sudoku using backtracking, look up Donald Knuth's DLX (dancing links) algorithm. It's a really interesting algorithm that can be used to solve a number of puzzles, and uses a linked "grid."

I'm addicted to solving Sudoku (just not by hand, but algorithmically)... constraint programming is another fun one to try: choco-solver in Java is a great library and it gives you a very nice taste of how constraint programming works, which is something that you could find useful in your code.

[TheJaguar]

When I did this for Codingame, I used a hybrid approach: use rules to solve until you can't, then choose a possible number to insert into a blank and use rules until it solves or breaks.

[Julian-vivl]

Nice, I wrote a similar sudoku solver a couple days ago and its a really fun problem
would recommend it to others.

[john_critchley]

Hm... I wrote a sudoku solver over Christmas... took me just less than 3 weeks... but I did do it in Z80 assembler; I was thinking of adding a similar bitmap mechanism across rows, columns and "blocks" but there are only 8 bits in the byte, so that would make doing 9 fiddly ... and I didn't bother doing further work on it as just checking across the locations was fast enough. I generate a lookup table for the cells in the "block" which are not covered by the row and column checks, so it only needs to check 4 cells per block. It now runs on a Z80 emulator _and_ on a RC2014 (real Z80 based retrocomputer). Perhaps I should do a video on how I wrote it.

[primeprover]

Would love to see a video showing the construction of a solver for a 16x16 sudoku. A little more thought is needed as brute force recursion is too slow.

[Kornchipzzz]

Subbed. Excited to see where this channel will go!

[JustinRiedyk]

Took me a second to work out why the Python code looked so bananas.

[etmax]

finally someone who indents and brackets properly 👍

[MatheusAugustoGames]

Very nice! I once used the same concept to solve the eight queens puzzle, it was very entertaining! I might try doing it in C++ now that I know bitsets are a thing :P

[qnn]

Amazing video, your coding style is so clean!

[kasparpoland]

this a great video. youtube knows it too bc i watched it when it dropped but it just got recommended it to me again.

[cameronguilbeau]

Really enjoy this content, keep it up.

[kylefluto]

James, could you do a video showing a formal proof and (hopefully) the intuition behind detecting the start of a cycle in a singly-linked list?

[lupomikti]

Had this as an assignment but in Prolog. I remember how the goal was just to program the brute force method and make sure it could solve hard ones in less than 5 minutes, but we could earn extra points if I made it more efficient with heuristics and movement through the board. Everyone was so shocked when I presented my solution and said it could solve all 5 of the given boards in less than a second haha xD Was the most fun assignment I had at uni.

[laurinneff]

I never heard of recursive backtracking before. I'd write a sudoku solver like this: loop over every square, for each of them find all possible solutions. If there's just one solution, fill it in, else don't do anything. Repeat until there are no squares left