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https://github.com/anowell/today-puzzle

Solution to a math puzzle
https://github.com/anowell/today-puzzle

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Solution to a math puzzle

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README 

        
### today-puzzle



I was intrigued by this puzzle at a local math event.



![Today-is math puzzle](today-puzzle.jpg)



So I decided to write a solution for it, and [blog about it](https://anowell.com/posts/calendar-puzzle.html).



And then extended it to work for similar puzzles.



If you just want solutions, check out the [**Interactive Solver**](https://anowell.github.io/today-puzzle/).



### Build/Run



today-puzzle is written in [Rust](https://rustup.rs/) and built with [cargo](https://doc.rust-lang.org/cargo/commands/build-commands.html).

Use [just](https://github.com/casey/just) or see the [Justfile](Justfile) for command helpers.



```

# Run to solve a specific date

# Each piece is represented by a unique letter

$ just run --date 12-25

**** 12-25 ****

A A G G G G . .

A A E E G . . .

A A E F B B B .

D D E F B H B .

C D E F F H H .

C D D . F H H .

C C C . . . . .

. . . . . . . .



# Run for all days, but only print the solution count

$ just run --all-dates --print count

01-01 has 64 solutions

01-02 has 109 solutions

01-03 has 47 solutions

01-04 has 103 solutions

...snip...



$ just run --help

Puzzle-a-day solver



Usage: today-is [OPTIONS]



Options:

  -d, --date 

          Date to solve in M-D format [default: today]



  -a, --all-dates

          Count solutions for every day of the year



  -p, --print 

          Specifies with solutions to print



          [default: first]



          Possible values:

          - first:   Display first solution, but no count (fastest)

          - summary: Display first solution and count of solutions

          - all:     Display all solutions and count of solutions

          - count:   Display only the count of solutions

          - check:   Only prints indicator if solution exists (exits early if any day is unsolvable)



  -v, --variant 

          Puzzle variant



          [default: dragon-fjord]

          [possible values: dragon-fjord, crea-makerspace, jarring-words, tetromino]



  -h, --help

          Print help information (use `-h` for a summary)



  -V, --version

          Print version information

```



It can also be built to target WASM using [wasm-pack](https://rustwasm.github.io/wasm-pack/installer/).

This example uses [miniserve](https://github.com/svenstaro/miniserve) to serve files:



```

$ just wasm



# start file server (e.g. uses miniserve - could use any file server)

$ just serve



```



Then you can open your browser to `localhost:8080` to see the interactive puzzle solver.



![Today-is solver](today-is-viz.png)



## Performance



On my Dell XPS 13 Plus (for the DragonFjord variant):



- It takes about 150ms to find all solutions for a given date (original implementation ~1s)

- It takes about 1s to find one solution for every day of the year (original implementation ~10s)

- It takes about 30s to find all solutions for every day of the year (original implementation ~6min)



Variant differences:



- The CreaMakerspace variant is the slowest to find a single solution per date, but the fastest to find all solutions (because it has the fewest solution per date on average).

- The Tetromino variant is the fastest to find a single solution per date, but the slowest to find all solutions (because it has the most solutions per date on average).



Optimizing:



Flamegraph (`just flamegraph`) shows the time is basically split between `BitPiece::to_bitboard` and `BitBoard::has_small_gaps`.



- `to_bitboard` was the original hot loop. It was optimized with benchmarks (`cargo bench`) in [benches/bitpiece_bench.rs](benches/bitpiece_bench.rs) with the original implementation ~1.8ns vs the current implementation arround 0.8ns. It may be possible to mostly eliminate this function by just storing pieces as `u64` instead of `u16`.

- `has_small_gaps` reduced the number of `to_bitboard` calls significantly. It's implementation accounted for 5-10x speedup.