Product of digits.

main.rs

use std::time::Instant;

fn split(mut n: u128) -> Vec<u8> {
    let mut elems: Vec<u8> = Vec::new();
    while n != 0 {
        let e = n % 10;
        elems.push(e as u8);
        n /= 10;
    }
    
    return elems;
}

fn count(mut n: u128) -> i32 {
    let mut cnt = 0;
    loop {
        let elems = split(n);
        if elems.len() <= 1 { break; }
        cnt += 1;
        n = elems.into_iter().fold(1, |acc: u128, x: u8| acc * (x as u128));
    }
    return cnt;
}

fn main() {
    let start_time = Instant::now();
    let mut cnt_max = 0;
    for n in 0_u128.. {
        let c = count(n);
        if c > cnt_max {
            println!("[Updated!!] {}: {} (Time Elapsed: {} sec)", n, count(n), start_time.elapsed().as_secs_f32());
            cnt_max = c;
        }
    }
}