projecteuler.net/040/main.rs

use std::str::FromStr;

fn ts(k: usize, s: &String) -> u32 {
    u32::from_str(s.chars().nth(k).unwrap().to_string().as_str()).unwrap()
}

fn main() {
    let mut res = String::from("0");
    let mut k = 1usize;
    while res.len() < 1000001 {
        res.push_str(k.to_string().as_str());
        k += 1;
    }
    
    println!("{}", ts(9, &res));
    let mut prod = 1;
    let mut i = 1;
    while i <= 1000000 {
        prod *= ts(i, &res);
        i *= 10;
    }
    println!("{}", prod);
}