About 8 years ago, I posted this: Stupid Coding Tricks: Sudoku solver in Whitespace!
Well, I may have "jumped the shark" by finally recreating my solver in Brainfuck: Sudoku.7z
Just as before, this was done as a test of a compiler for a high-level language I designed (it's a bit like C, but supports generics on struct types).
Unfortunately, it doesn't seem to work well in online brainfuck interpreters - uncompressed it's a 3.75 MB program, and for some reason crashes Chrome when I try to paste it all into a text box.
If you're interested, it seems to work great on the optimizing Brainfuck to Python compiler bfc.py posted here: https://www.nayuki.io/page/optimizing-brainfuck-compiler although I'm sure it'll work on pretty much any compiler/interpreter.