Compute letters frequencies in a string

count.rs

use std::collections::BTreeMap;

fn main() {
    let text = "abbcbbaaeef";
    let mut scores = BTreeMap::new();
    for c in text.chars() {
        scores.entry(c).and_modify(|e| *e += 1).or_insert(1);
    }
    for (k, v) in scores {
        println!("{}: {}", k, v);
    }
}