bytearray solution

wordcount.rs

use std::io::{self, Read, Write, BufWriter};
use std::collections::HashMap;

fn main() {
    let mut buffer = Vec::<u8>::new();
    io::stdin().read_to_end(&mut buffer).ok();

    let mut words: HashMap<&[u8], usize> = HashMap::new();
    for word in buffer.split(is_whitespace).filter(is_not_empty) {
        if let Some(count) = words.get_mut(word) {
            *count += 1;
            continue;
        }
        words.insert(word, 1);
    }

    let mut multiple: Vec<(&[u8], usize)> = vec![];
    let mut single: Vec<(&[u8], usize)> = vec![];

    for (word, count) in words.iter() {
        if *count > 1 {
            multiple.push((*word, *count));
        } else {
            single.push((*word, *count));
        }
    }

    multiple.sort_by_key(|a| a.0);
    multiple.sort_by(|a, b| b.1.cmp(&a.1));
    single.sort_by_key(|a| a.0);

    let mut output = BufWriter::new(io::stdout());
    unsafe {
        for word in multiple {
            writeln!(output, "{}\t{}", std::str::from_utf8_unchecked(word.0), word.1).ok();
        }

        for word in single {
            writeln!(output, "{}\t{}", std::str::from_utf8_unchecked(word.0), word.1).ok();
        }
    }
}
#[inline]
fn is_whitespace(c: &u8) -> bool {
    *c == b' ' || *c == b'\t' || *c == b'\n'
}

#[inline]
fn is_not_empty(s: &&[u8]) -> bool {
    !s.is_empty()
}