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use rand::distributions::{Distribution, WeightedIndex};
use rand::RngCore;
const NUM_OF_LETTERS: usize = 26;
pub struct Model {
chars: [[usize; NUM_OF_LETTERS + 1]; NUM_OF_LETTERS + 1],
}
impl Model {
pub fn new() -> Model {
let chars = include!(concat!(env!("OUT_DIR"), "/prebuilt_model.rs"));
Model { chars }
}
pub fn generate<Rng: RngCore>(
&self,
rng: &mut Rng,
len: usize,
first_char: Option<char>,
) -> String {
let mut result = String::with_capacity(len);
let mut prefix = first_char
.map(|c| c as usize - b'a' as usize)
.unwrap_or(NUM_OF_LETTERS);
for _ in 0..len {
let chars = &self.chars[prefix];
let c = select_one_char(rng, chars);
result.push(c as char);
prefix = (c - b'a') as usize;
}
result
}
}
fn select_one_char<Rng: RngCore>(rng: &mut Rng, freq: &[usize; NUM_OF_LETTERS + 1]) -> u8 {
let dist = WeightedIndex::new(freq).expect("invalid frequency");
b'a' + (dist.sample(rng) as u8)
}
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