Rust BTreeMap and BTreeSet

In rust

• the std::collections::BTreeMap is the implementation of a sorted map.
• the std::collections::BTreeSet is the implementation of a sorted set.

Floor and Ceil

Floor: The Entry with the Greatest Key that is Less or Equal to a Given Key

#![allow(unused)]
fn main() {
map.range(..=key).next_back().unwrap();
}

Ceil: The Entry with the Least key that is Greater or Equal to a Given Key

#![allow(unused)]
fn main() {
map.range(key..).next().unwrap();
}

First

#![allow(unused)]
fn main() {
let set = BTreeSet::from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
// unstable approach: need `#![feature(map_first_last)]` feature flag
println!("{:?}", set.first());
// current approach:
println!("{:?}", set.range(..).next());
}

Last

#![allow(unused)]
fn main() {
let set = BTreeSet::from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
// unstable approach: need `#![feature(map_first_last)]` feature flag
println!("{:?}", set.last());
// current approach:
println!("{:?}", set.range(..).next_back());
}

Remove all elements in a given range

NOTE: This might not be the most idiomatic rust approach

Instead of removing elements from the range one by one, we have to filter out of the element in the range and then re-create the tree-map.

use std::collections::BTreeMap;

fn main() {
    let mut map: BTreeMap<usize, usize> = BTreeMap::new();
    map.insert(10, 10);
    map.insert(20, 20);
    map.insert(30, 30);
    map.insert(40, 40);
    map.insert(50, 50);

    map = map
        .into_iter()
        .filter(|(key, _)| *key < 20 || *key >= 40)
        .collect();

    println!("{:?}", map);
}

How does it work?

#![allow(unused)]
fn main() {
pub fn range<T, R>(&self, range: R) -> Range<'_, K, V>
}

BTreeMap has an range method that takes a range as input and will output all the entries from the map with a key that is within the given range.

use std::collections::BTreeSet;

fn main() {
let set = BTreeSet::from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);

// [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
let res = set.range(..);
println!("{:?}", res);

// [5, 6, 7, 8, 9]
let res = set.range(5..);
println!("{:?}", res);

// [0, 1, 2, 3, 4]
let res = set.range(..5);
println!("{:?}", res);

// [0, 1, 2, 3, 4, 5]
let res = set.range(..=5);
println!("{:?}", res);

// [4, 5, 6]
let res = set.range(4..=6);
println!("{:?}", res);
}