pub fn day7_part1(input: &str) -> String {
    emit_tachyon(input).0.to_string()
}
pub fn day7_part2(input: &str) -> String {
    emit_tachyon(input).1.to_string()
}

fn emit_tachyon(input: &str) -> (u64, u64) {
    let (start_col, splittermap) = parse(input);
    let mut beam_cols = vec![0; splittermap[0].len()];
    beam_cols[start_col] = 1;
    let mut splitcount = 0;

    for splitter_row in splittermap {
        let mut next_beam_cols = vec![0; splitter_row.len()];
        next_beam_cols[0] = beam_cols[0];
        next_beam_cols[splitter_row.len() - 1] = beam_cols[splitter_row.len() - 1];
        for col in 1..splitter_row.len() - 1 {
            if splitter_row[col] {
                next_beam_cols[col - 1] += beam_cols[col];
                next_beam_cols[col + 1] += beam_cols[col];
                if beam_cols[col] != 0 {
                    splitcount += 1;
                }
            } else {
                next_beam_cols[col] += beam_cols[col]
            }
        }
        beam_cols = next_beam_cols;
    }
    (splitcount, beam_cols.into_iter().sum())
}

//true: splitter
fn parse(input: &str) -> (usize, Vec<Vec<bool>>) {
    let start_col = input
        .chars()
        .enumerate()
        .find(|(_, c)| *c == 'S')
        .unwrap()
        .0;
    let splittermap = input
        .lines()
        .map(|l| l.chars().map(|c| c == '^').collect())
        .collect();
    (start_col, splittermap)
}