io performance example

main.rs

use std::{
    collections::{BTreeMap, HashMap},
    error::Error,
    io::{self, Read},
};

use time::Instant;

fn main() -> Result<(), Box<dyn Error>> {
    let o_start = Instant::now();
    let r_start = Instant::now();
    let mut buffer = String::new();
    let _ = io::stdin().read_to_string(&mut buffer)?;
    let r_read = r_start.elapsed();

    let p_start = Instant::now();
    let buffer = buffer.to_lowercase();
    let mut words = HashMap::<&str, usize>::new();
    for word in buffer.split_whitespace() {
        match words.get_mut(word) {
            Some(count) => {
                *count = *count + 1;
            }
            None => {
                words.insert(word, 1);
            }
        }
    }

    let p_read = p_start.elapsed();

    let s_start = Instant::now();
    let mut sorted_words: Vec<_> = words
        .iter()
        .map(|(k, v)| CountedWord { word: k, count: &v })
        .collect();
    sorted_words.sort_by(|f1, f2| f2.count.cmp(f1.count));
    let s_read = s_start.elapsed();

    let w_start = Instant::now();
    for CountedWord { word, count } in sorted_words {
        println!("{word}{count}");
    }
    let w_read = w_start.elapsed();

    let o_read = o_start.elapsed();

    eprintln!("Reading: {}", r_read.as_seconds_f64());
    eprintln!("Processing: {}", p_read.as_seconds_f64());
    eprintln!("Sorting: {}", s_read.as_seconds_f64());
    eprintln!("Outputting: {}", w_read.as_seconds_f64());
    eprintln!("Overall: {}", o_read.as_seconds_f64());

    Ok(())
}

struct CountedWord<'a> {
    word: &'a str,
    count: &'a usize,
}