Code shared from the Rust Playground

playground.rs

use std::collections::BTreeMap;
fn main() {
    // Let's create a nested B-tree structure:
    // A BTreeMap where keys are strings (e.g., "country")
    // and values are another BTreeMap (e.g., "city" -> population).
    let mut world_populations: BTreeMap<String, BTreeMap<String, u64>> = BTreeMap::new();

    // Add some data for "USA"
    let mut usa_cities = BTreeMap::new();
    usa_cities.insert("New York".to_string(), 8_468_000);
    usa_cities.insert("Los Angeles".to_string(), 3_898_000);

    world_populations.insert("USA".to_string(), usa_cities);

    // Add some data for "India"
    let mut india_cities = BTreeMap::new();
    india_cities.insert("Mumbai".to_string(), 20_667_000);
    india_cities.insert("Delhi".to_string(), 32_941_000);

    world_populations.insert("India".to_string(), india_cities);

    // Accessing the data
    if let Some(cities) = world_populations.get("USA") {
        if let Some(population) = cities.get("New York") {
            println!("The population of New York is: {}", population);
        }
    }
}