Rust Platform

In Python, sets provide unique collections with fast membership testing:

tags = {"rust", "python", "coding"}
tags.add("rust")  # no duplicate
print("rust" in tags)  # O(1) lookup

a = {1, 2, 3}
b = {2, 3, 4}
print(a & b)  # intersection: {2, 3}
print(a | b)  # union: {1, 2, 3, 4}
print(a - b)  # difference: {1}

Rust's HashSet<T> works the same way.

Creating and using HashSet

use std::collections::HashSet;

let mut tags: HashSet<String> = HashSet::new();
tags.insert("rust".to_string());
tags.insert("rust".to_string());  // ignored - already exists
assert_eq!(tags.len(), 1);

if tags.contains("rust") {
    println!("Found it!");
}

Set operations

let a: HashSet<i32> = [1, 2, 3].into_iter().collect();
let b: HashSet<i32> = [2, 3, 4].into_iter().collect();

let intersection: HashSet<_> = a.intersection(&b).copied().collect();
let union: HashSet<_> = a.union(&b).copied().collect();
let difference: HashSet<_> = a.difference(&b).copied().collect();

From iterator

let numbers = vec![1, 2, 2, 3, 3, 3];
let unique: HashSet<i32> = numbers.into_iter().collect();
assert_eq!(unique.len(), 3);

Your Task

1. unique_items(items: Vec<i32>) -> Vec<i32> — return unique items (preserve order of first occurrence)
2. common_elements(a: &[i32], b: &[i32]) -> Vec<i32> — find elements in both (sorted output)
3. is_subset(subset: &[i32], superset: &[i32]) -> bool — check if all elements of subset are in superset