use std::collections::HashMap;

fn main(){
    let mut trees : HashMap<&str, u32> = HashMap::new();
    trees.insert("Oak", 5);
    trees.insert("Sycamore", 30);
    trees.insert("Elm", 20);

    *trees.entry("Elm").or_insert(0) += 2;

    let maple_ref : &mut u32 = trees.entry("Maple").or_insert(0);
    *maple_ref = 47;


    for (key, value) in trees {
        println!("{}: {}", key, value);
    }



}