You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: cellular_automata.rs
    path of file: ./repos/rustrogueliketutorial/chapter-36-layers/src/map_builders
    
    the code of the file until where you have to start completion: use super::{InitialMapBuilder, BuilderMap, TileType};
use rltk::RandomNumberGenerator;

pub struct CellularAutomataBuilder {}

impl InitialMapBuilder for CellularAutomataBuilder {
    #[allow(dead_code)]
    fn build_map(&mut self, rng: &mut rltk::RandomNumberGenerator, build_data : &mut BuilderMap) {
        self.build(rng, build_data);
    }
}

impl CellularAutomataBuilder {
    #[allow(dead_code)]
    pub fn new() -> Box<CellularAutomataBuilder> {
        Box::new(CellularAutomataBuilder{})
    }

    #[allow(clippy::map_entry)]
    fn build(&mut self, rng : &mut RandomNumberGenerator, build_data : &mut BuilderMap) {
        // First we completely randomize the map, setting 55% of it to be floor.
        for y in 1..build_data.map.height-1 {
            for x in 1..build_data.map.width-1 {
                let roll = rng.roll_dice(1, 100);
                let idx = build_data.map.xy_idx(x, y);
                if roll > 55 { build_data.map.tiles[idx] = TileType::Floor }
                else { build_data.map.tiles[idx] = TileType::Wall }
            }
        }
        build_data.take_snapshot();

        // Now we iteratively apply cellular automata rules
        for _i in 0..15 {
            let mut newtiles =
    
    fn build(&mut self, rng : &mut RandomNumberGenerator, build_data : &mut BuilderMap) {
        // First we completely randomize the map, setting 55% of it to be floor.
        for y in 1..build_data.map.height-1 {
            for x in 1..build_data.map.width-1 {
                let roll = rng.roll_dice(1, 100);
                let idx = build_data.map.xy_idx(x, y);
                if roll > 55 { build_data.map.tiles[idx] = TileType::Floor }
                else { build_data.map.tiles[idx] = TileType::Wall }
            }
        }
        build_data.take_snapshot();

        // Now we iteratively apply cellular automata rules
        for _i in 0..15 {
            let mut newtiles = build_data.map.tiles.clone();

            for y in 1..build_data.map.height-1 {
                for x in 1..build_data.map.width-1 {
                    let idx = build_data.map.xy_idx(x, y);
                    let mut neighbors = 0;
                    if build_data.map.tiles[idx - 1] == TileType::Wall { neighbors += 1; }
                    if build_data.map.tiles[idx + 1] == TileType::Wall { neighbors += 1; }
                    if build_data.map.tiles[idx - build_data.map.width as usize] == TileType::Wall { neighbors += 1; }
                    if build_data.map.tiles[idx + build_data.map.width as usize] == TileType::Wall { neighbors += 1; }
                    if build_data.map.tiles[idx - (build_data.map.width as usize - 1)] == TileType::Wall { neighbors += 1; }
                    if build_data.map.tiles[idx - (build_data.map.width as usize + 1)] == TileType::Wall { neighbors += 1; }
                    if build_data.map.tiles[idx + (build_data.map.width as usize - 1)] == TileType::Wall { neighbors += 1; }
                    if build_data.map.tiles[idx + (build_data.map.width as usize + 1)] == TileType::Wall { neighbors += 1; }

                    if neighbors > 4 || neighbors == 0 {
                        newtiles[idx] = TileType::Wall;
                    }
                    else {
                        newtiles[idx] = TileType::Floor;
                    }
                }
            }

            build_data.map.tiles = newtiles.clone();
            build_data.take_snapshot();
        }
    }