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The Robosnake was Redbrick's bounty snake entry for the 2017 Battlesnake AI programming competition. It is written using Lua and designed to be run under OpenResty.
Our win conditions to claim the bounty were the following:
- Game is played on a 17 x 17 board
- 10 food are present on the board, at any given time
- API timeout of 1 second
- One-versus-one, last snake slithering wins the bounty.
Under these conditions, we won forty-two games and lost three, for a total win record of 42/45 or 93%.
The Robosnake makes use of alpha-beta pruning in order to make predictions about the future state of the game. All possible moves by ourselves are evaluated, as well as all possible moves by the enemy. The Robosnake will always select for itself the move that results in the best possible state of the game board, and it will select for the enemy the move that results in the worst possible state of the game board (from the Robosnake's point of view, that is).
In order to evaluate a particular game board state, we look at the following metrics to produce a numeric score:
- How much health do I have?
- How much health does the enemy have?
- How many moves are available to me from my current position?
- How many moves are available to the enemy from its' current position?
- How many free squares can I see from my current position? (flood fill)
- How many free squares can the enemy see from its' current position? (another flood fill)
- How close am I to food right now?
In the event that we're playing in an arena containing more than one enemy snake, the closest snake to the Robosnake will be chosen as the "enemy" for the purposes of algorithmic computation.
In the event that we're playing in an empty arena, the Robosnake will choose itself as the "enemy". This will often lead to hilarity.
A blog post that talks about the strategy in depth is here: https://rdbrck.com/2017/03/building-bounty-snake-post-mortem/
Configuration is done in /config/http.conf.
RULES_VERSION- this can be set to2016or2017.MAX_RECURSION_DEPTH- this affects how far the alpha-beta pruning algorithm will look ahead. Increasing this will make the Robosnake much smarter, but response times will be much longer.SNAKE_ID- when using2016rules, this needs to be set to the ID sent by the Battlesnake client.