Rust the book exercises in https://doc.rust-lang.org/book/second-edition/ch08-03-hash-maps.html

8-3-1.rs

// 参考： https://codereview.stackexchange.com/questions/173338/calculate-mean-median-and-mode-in-rust
use std::collections::HashMap;
fn mean(data : &Vec<i32>) -> f32 {
    let mut r = 0;
    for i in data {
        r = r + i;
    }
    r as f32 / data.len() as f32
}
fn median(data: &Vec<i32>) -> i32 {
    let mut work = data.clone();
    work.sort();
    work[data.len() / 2]
}
fn mode(data: &Vec<i32>) -> (i32, i32) {
    let mut map:HashMap<&i32, i32> = HashMap::new();
    for i in data {
        let count = map.entry(i).or_insert(0);
        *count += 1;
    }
    let mut count_vec: Vec<(&&i32,&i32)> = map.iter().collect();
    count_vec.sort_by(|a,b| b.1.cmp(a.1)); 
    (**count_vec[0].0, *count_vec[0].1) // I do not think this is not optimal...
}
fn main() {
    let d = vec![9,129,53,899,1,2,4,4,31,9,129,53,53];
    println!("mean: {}", mean(&d));
    println!("median: {}", median(&d));
    let m = mode(&d);
    println!("mode: {} ( {} times )", m.0, m.1);

}

8-3-2.rs

fn piglatin(s: &str) -> String {
    let s = s.to_string();
    let mut si = s.chars();
    let mut post = String::new();
    let mut pre = String::new();
    while let Some(c) = si.next() {
        match c {
            'a' | 'e' | 'i' | 'o' | 'u' => {
                pre.push(c);
                break;
            }
            _ => {
                post.push(c);
            }
        }
    }
    let s : String = si.collect();
    pre = pre + s.as_str();
    if post.len() == 0 {
       post.push('h');
    }
    format!("{}-{}ay",pre, post)
}
fn main() {
    println!("{}", piglatin("apple"));
}