use std::time::Instant;


/** @return `msg` duplicated `n` times. */
fn string_times( n: u32,  msg: &str ) -> String {
    let mut result_so_far: String = String::from("");
    for _i in 0..n {
        result_so_far.push_str(msg);
        }
    result_so_far
    }


fn main() {
    let mut v:Vec<u8> = Vec::new();
    v[0] = b'a';
    v[1] = b'z';
    println!("{:?}", v);


    println!("Hello, world!");
    println!("{}", string_times(3, "echo!"));
    

    
    for tst in vec![ (      100,"a"),
                     (    1_000, "a"),
                     (   10_000, "a"),
                     (  100_000, "a"),
                     (      100, "abcde"),
                     (    1_000, "abcde"),
                     (   10_000, "abcde"),
                     (  100_000, "abcde"),
                     (1_000_000, "abcde"),
                     (1_000_000, "a"),
                     (10_000_000, "abcde"),
                     (100_000_000, "abcde"),
                     ] {
        let k: u32 = tst.0;
        let msg: String = String::from(tst.1);
        let t0 = Instant::now();
        string_times( tst.0, tst.1 );
        let t1 = Instant::now();
        println!( "{:>9}x{:>9} requires {:>9}ms.", 
                  k, msg.len(), t1.duration_since(t0).as_millis() );
            }
    }




// Want to say: the running-time of this function is O(n * msg.length()).
/***************/