# 2048-rust

A 2048 implementation that uses bit-shifting and a pre-computed move table this implementation is designed to provide low overhead when testing an algorithm on a large amount of games. On a mid-2015 MBP Retina (2.5GHz i7) 10,000,000 games take about 80 seconds to complete running on 8 threads (1,250,000 games per thread) by executing random moves, avg score ~2k.

The board itself is encoded as a u64. This means that each tile has 4 bits (64 / 16 = 4) to store its value. Since the maximum value of setting all four bits to 1 is 15 we cannot use it to display the value directly. Instead we use these 4 bits as the power value: `2 << 15 = 65536`, `2 << 14 = 32768`, `2 << 13 = 16384`, `2 << 12 = 8192`, etc...

## Installation

Add the following to your `Cargo.toml` file:

```toml
[dependencies]
tfe = "0.1"
```

## Usage

A simple way to play the game automatically is to use the `tfe::Game::play` method:

```rust
extern crate tfe;
use tfe::{Game, Direction};

// Direction enum contains the following valid moves:
// - Direction::Left
// - Direction::Right
// - Direction::Down
// - Direction::Up

let game = Game::play(|board, failed| Direction::sample_without(failed));
println!("score: {:<6} board hex: {:016x}", Game::score(game.board), game.board);
```

The play method takes a closure that accepts a `board: u64` and `failed: &Vec<Direction>` as parameters and returns the next `Direction` to move in.

The game will terminate if each distinct move has been attempted and failed without any successfull move in between.

## Documentation

The documentation for this crate can be found [here on docs.rs](https://docs.rs/tfe).

## References

I certainly did not invent this implementation, large parts are taken from @nneonneo's implementation in c++.

Honorable mentions to good references:

- https://github.com/nneonneo/2048-ai/blob/master/2048.h
- https://github.com/nneonneo/2048-ai/blob/master/2048.cpp
- https://stackoverflow.com/questions/22342854/what-is-the-optimal-algorithm-for-the-game-2048