BTreeMap

Use an ordered-key map with BTreeMap.

BTreeMap

BTreeMap<K, V> is also a key-value table, but it keeps the keys sorted. Lookup is O(log n); iteration is always in key order. The key type must be Ord:

use std::collections::BTreeMap;

let mut m = BTreeMap::new();
m.insert("zeytin", 3);
m.insert("armut", 5);
m.insert("muz", 2);
for (k, v) in &m {
    println!("{k}={v}");   // in the order armut, muz, zeytin
}

Range queries

The sorted structure gives cheap access to range queries and extreme values:

let mut sicaklik = BTreeMap::new();
for (saat, d) in [(8, 12), (12, 21), (15, 24), (20, 16)] {
    sicaklik.insert(saat, d);
}
let ogleden_sonra: Vec<_> = sicaklik.range(12..=18).collect();
println!("{:?}", ogleden_sonra);            // [(12, 21), (15, 24)]
println!("{:?}", sicaklik.first_key_value()); // Some((8, 12))

Exercise Sorted list

Insert ("zeytin", 3), ("armut", 5) and ("muz", 2) into a BTreeMap; print the pairs as key=value, one per line.

Show example solution

use std::collections::BTreeMap;

fn main() {
    let mut m = BTreeMap::new();
    m.insert("zeytin", 3);
    m.insert("armut", 5);
    m.insert("muz", 2);
    for (k, v) in &m {
        println!("{}={}", k, v);
    }
}

Test yourself

In which case is BTreeMap a better fit than HashMap?
- When results must be reported in key order
- When the fastest single lookup is needed
- When keys implement Hash but not Ord
- Never
Show answer

When results must be reported in key order — BTreeMap for sorted output, range queries and smallest/largest key; HashMap for raw speed.

Query by range

let secim: Vec<_> = sicaklik.____(12..=18).collect();

Show answer

let secim: Vec<_> = sicaklik.range(12..=18).collect();

Feature and structure

Ordered iteration

BTreeMap
Ortalama O(1) arama

HashMap
range(a..b)

BTreeMap (only)
Anahtar Hash + Eq

HashMap requirement

Next lesson: HashSet

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