counter.rs

use std::time::SystemTime;

fn main() {
    let letters: String = (b'a'..b'z' + 1).map(|c| c as char).collect();
    let repeated = letters.repeat(1000_0000);

    let now = SystemTime::now();
    let mut rslt: Vec<_> = (0..26).map(|_| 0).collect();
    for ch in repeated.chars() {
        let pos = ch as usize - 'a' as usize;
        rslt[pos] += 1;
    }

    for (idx, val) in rslt.iter().enumerate() {
        print!("{}: {}", ((idx + 'a' as usize) as u8) as char, val);
    }

    let elapsed = now.elapsed().unwrap();
    println!("\ntime: {}.{:09}s ",
             elapsed.as_secs(),
             elapsed.subsec_nanos());
}