Rust Interview Questions and Answers

Hey there! If you’re prepping for a Rust interview, you’re in the right place. I’ve put together a mix of basic, coding, advanced, and behavioral questions to help you nail it. Let’s dive in!

Basic Rust Interview Questions

Q1: What’s the deal with ownership rules in Rust?

Answer: Ownership is Rust’s secret sauce for memory safety without needing a garbage collector. Here’s the rundown:

1. Every value has one owner—like a VIP pass to memory.
2. When that owner goes out of scope, Rust cleans up the memory automatically. No fuss, no muss.
3. You can pass ownership to someone else (called a “move”) or let others peek at it temporarily (borrowing), either immutably or mutably.
   It’s all about keeping things tidy and safe!

Q2: How does move differ from copy in Rust?

Answer:

• Move: Think of it like handing over the keys to your car. Ownership transfers, and the original variable can’t use it anymore.
• Copy: This is just for simple stuff like numbers or booleans that implement the Copy trait. It’s like making a photocopy—both versions stick around.

Here’s an example:

rust

let x = String::from("hello");  
let y = x; // x gives up ownership to y, so x is done  
// println!("{}", x); // Nope, this would error!  

Q3: What’s borrowing all about in Rust?

Answer: Borrowing is like borrowing a book from a friend—you get to read it, but you don’t own it. In Rust, it’s temporary access to a value without taking it over.

Check this out:

rust

fn print_str(s: &String) {  
    println!("{}", s);  
}  

let s = String::from("hello");  
print_str(&s); // s is borrowed here, still good to use after  

Q4: Mutable vs. immutable borrowing—what’s the difference?

Answer:

• Immutable Borrowing (&): You can have as many read-only peeks as you want, but no changes allowed.
• Mutable Borrowing (&mut): Only one borrower at a time, and they can tweak the data.

Here’s a quick demo:

rust

let mut s = String::from("hello");  
let r1 = &s; // immutable borrow  
let r2 = &s; // another immutable borrow—totally fine  
// let r3 = &mut s; // Nope! Can’t mutate while others are borrowing  

Rust Coding Interview Questions

Q5: How would you reverse a string in Rust?

Answer: Here’s a clean way to flip a string:

rust

fn reverse_string(s: &str) -> String {  
    s.chars().rev().collect()  
}  

fn main() {  
    let input = "hello";  
    println!("{}", reverse_string(input)); // Prints "olleh"  
}  

It’s simple: break the string into characters, reverse them, and glue them back together!

Q6: How do you find the largest number in an array?

Answer: Rust makes this a breeze with iterators:

rust

fn find_largest(arr: &[i32]) -> i32 {  
    *arr.iter().max().unwrap()  
}  

fn main() {  
    let numbers = [3, 5, 9, 1, 4];  
    println!("Largest number: {}", find_largest(&numbers)); // 9  
}  

The unwrap() assumes there’s at least one number—otherwise, it’d panic.

Q7: Can you whip up a linked list in Rust?

Answer: Sure thing! Here’s a basic take using Rc and RefCell for flexibility:

rust

use std::rc::Rc;  
use std::cell::RefCell;  

struct Node {  
    value: i32,  
    next: Option<Rc<RefCell<Node>>>,  
}  

impl Node {  
    fn new(value: i32) -> Rc<RefCell<Node>> {  
        Rc::new(RefCell::new(Node { value, next: None }))  
    }  
}  

This sets up a node you can link up later. Rust’s safety rules make this trickier than in other languages, but it’s doable!

Q8: How about a thread-safe counter?

Answer: Let’s use Arc and Mutex to keep things safe across threads:

rust

use std::sync::{Arc, Mutex};  
use std::thread;  

fn main() {  
    let counter = Arc::new(Mutex::new(0));  
    let mut handles = vec![];  

    for _ in 0..10 {  
        let counter = Arc::clone(&counter);  
        let handle = thread::spawn(move || {  
            let mut num = counter.lock().unwrap();  
            *num += 1;  
        });  
        handles.push(handle);  
    }  

    for handle in handles {  
        handle.join().unwrap();  
    }  

    println!("Final count: {}", *counter.lock().unwrap()); // Should be 10  
}  

Each thread bumps the counter, and Mutex ensures no one steps on anyone else’s toes.

Q9: How would you code the Fibonacci sequence recursively?

Answer: Here’s a classic recursive Fibonacci:

rust

fn fibonacci(n: u32) -> u32 {  
    match n {  
        0 => 0,  
        1 => 1,  
        _ => fibonacci(n - 1) + fibonacci(n - 2),  
    }  
}  

fn main() {  
    println!("Fibonacci(10): {}", fibonacci(10)); // 55  
}  

It’s straightforward but not super efficient for big numbers—something to keep in mind!

Q10: How does Rust keep memory safe without a garbage collector?

Answer: Rust pulls this off with some clever tricks:

1. Ownership: One boss per value, and when they’re done, the memory’s freed.
2. Borrow Checker: It’s like a referee making sure no one messes up references or races for data.
3. RAII: Resources get cleaned up automatically when they’re no longer needed.
   No garbage collector, just strict rules that work like magic.

Rust Advanced Topics interview

Q11: What are lifetimes in Rust?

Answer: Lifetimes are Rust’s way of making sure references don’t outlive what they point to. Here’s an example:

rust

fn longest<'a>(s1: &'a str, s2: &'a str) -> &'a str {  
    if s1.len() > s2.len() { s1 } else { s2 }  
}  

The ‘a says both inputs and the output share the same lifespan—no dangling pointers allowed!

Q12: What’s the scoop on smart pointers?

Answer: Smart pointers give you more control over memory:

• Box<T>: Puts stuff on the heap with single ownership.
• Rc<T>: Lets multiple owners share something via reference counting.
• RefCell<T>: Sneaky way to mutate data even when it’s borrowed immutably.
  They’re like tools in your Rust toolbox for different jobs.

Q13: What’s up with async/await in Rust?

Answer: Async lets Rust handle tasks without blocking, using async and .await:

rust

async fn fetch_data() -> String {  
    "Hello, async!".to_string()  
}  

#[tokio::main]  
async fn main() {  
    let data = fetch_data().await;  
    println!("{}", data);  
}  

You’ll need a runtime like Tokio to make it work—it’s perfect for I/O-heavy stuff!

Q14: How does Rust fit into blockchain?

Answer: Rust is a rockstar in blockchain (think Solana or Substrate) because:

• It’s fast—no garbage collection slowing things down.
• It’s safe—fewer bugs and exploits.
• It handles concurrency like a champ, great for blockchain nodes.
  You might use it for smart contracts with frameworks like Anchor on Solana.

Behavioral & Problem-Solving Questions

Q15: How do you make Rust code run faster?

Answer: Here are some pro tips:

• Use iter() for loops instead of indexing—it’s slicker.
• Try Cow<T> (Clone-on-Write) to save memory when you don’t need copies.
• Cut down on heap allocations where you can.
• Profile with cargo flamegraph to spot bottlenecks.
  It’s all about working smarter, not harder!