Rust code shared from the playground

playground.rs

use std::collections::VecDeque;

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
enum State { A, B, C, D, E, F }
// enum State { A, B }

const ITERATIONS: usize = 12_459_852;
// const ITERATIONS: usize = 6;

fn main() {
    let mut tape = VecDeque::new();
    tape.push_back(false);
    let mut cursor = 0;
    let mut state = State::A;
    
    for _ in 0..ITERATIONS {
        // println!("({}, {:?}): {:?}", cursor, state, tape);
        
        // sample
        /*
        let (new_val, cursor_change, new_state) = match (state, tape[cursor]) {
            (State::A, false) => (true,   1, State::B),
            (State::A, true)  => (false, -1, State::B),
            (State::B, false) => (true,  -1, State::A),
            (State::B, true)  => (true,   1, State::A),
        };
        */
        
        let (new_val, cursor_change, new_state) = match (state, tape[cursor]) {
            (State::A, false) => (true,   1, State::B),
            (State::A, true)  => (true,  -1, State::E),
            (State::B, false) => (true,   1, State::C),
            (State::B, true)  => (true,   1, State::F),
            (State::C, false) => (true,  -1, State::D),
            (State::C, true)  => (false,  1, State::B),
            (State::D, false) => (true,   1, State::E),
            (State::D, true)  => (false, -1, State::C),
            (State::E, false) => (true,  -1, State::A),
            (State::E, true)  => (false,  1, State::D),
            (State::F, false) => (true,   1, State::A),
            (State::F, true)  => (true,   1, State::C),
        };
        
        state = new_state;
        tape[cursor] = new_val;
        if cursor == 0 && cursor_change == -1 {
            tape.push_front(false);
        } else {
            cursor = (cursor as isize + cursor_change) as usize;
        }
        if cursor == tape.len() {
            tape.push_back(false);
        }
    }
    
    let checksum = tape.iter().filter(|&&b| b).count();
    println!("{}", checksum);
}