Fastest I know

main.rs

use std::collections::HashMap;
use std::io::{self, prelude::*};

struct Counter {
    items: HashMap<String, usize>,
}

impl Counter {
    fn new() -> Counter {
        return Counter {
            items: HashMap::with_capacity(1000),
        };
    }
    fn add(&mut self, st: &str) {
        match self.items.get_mut(st) {
            Some(x) => {
                *x += 1;
            }
            None => {
                self.items.insert(st.to_owned(), 1);
            }
        }
    }

    fn render(&self) {
        for (key, val) in &self.items {
            println!("{}\t{}", val, key);
        }
    }
}

fn main() -> Result<(), io::Error> {
    let mut c = Counter::new();

    let mut line = String::new();
    let stdin = io::stdin();
    let mut stdin_lock = stdin.lock();
    while stdin_lock.read_line(&mut line)? != 0 {
        c.add(line.trim_end());
        line.clear();
    }

    c.render();

    Ok(())
}