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Print a literal string on standard output
println!("Hello World");
Loop to execute some code a constant number of times
for _ in 0..10 { println!("Hello"); }
Alternative implementation:
print!("{}", "Hello\n".repeat(10));
Like a function which doesn't return any value, thus has only side effects (e.g. Print to standard output)
fn finish(name: &str) {
    println!("My job here is done. Goodbye {}", name);
Create a function which returns the square of an integer
fn square(x : u32) -> u32 { x * x }
Declare a container type for two floating-point numbers x and y
struct Point {
    x: f64,
    y: f64,
Alternative implementation:
struct Point(f64, f64);
Do something with each item x of the list (or array) items, regardless indexes.
for x in items {
Alternative implementation:
items.into_iter().for_each(|x| do_something(x));
Print each index i with its value x from an array-like collection items
for (i, x) in items.iter().enumerate() {
    println!("Item {} = {}", i, x);
Alternative implementation:
items.iter().enumerate().for_each(|(i, x)| {
    println!("Item {} = {}", i, x);
Create a new map object x, and provide some (key, value) pairs as initial content.
let mut x = BTreeMap::new();
x.insert("one", 1);
x.insert("two", 2);
Alternative implementation:
let x: HashMap<&str, i32> = [
    ("one", 1),
    ("two", 2),
The structure must be recursive because left child and right child are binary trees too. A node has access to children nodes, but not to its parent.
struct BinTree<T> {
    value: T,
    left: Option<Box<BinTree<T>>>,
    right: Option<Box<BinTree<T>>>,
Generate a random permutation of the elements of list x
let mut rng = StdRng::new().unwrap();
rng.shuffle(&mut x);
Alternative implementation:
let mut rng = thread_rng();
x.shuffle(&mut rng);
The list x must be non-empty.
Alternative implementation:
let mut rng = rand::thread_rng();
let choice = x.choose(&mut rng).unwrap();
Check if the list contains the value x.
list is an iterable finite container.
Alternative implementation:
list.iter().any(|v| v == &x)
Alternative implementation:
(&list).into_iter().any(|v| v == &x)
Alternative implementation:
Access each key k with its value x from an associative array mymap, and print them.
for (k, x) in &mymap {
    println!("Key={key}, Value={val}", key=k, val=x);
Pick a random number greater than or equals to a, strictly inferior to b. Precondition : a < b.
Pick a random integer greater than or equals to a, inferior or equals to b. Precondition : a < b.
fn pick(a: i32, b: i32) -> i32 {
    let between = Range::new(a, b);
    let mut rng = rand::thread_rng();
    between.ind_sample(&mut rng)
Alternative implementation:
Uniform::new_inclusive(a, b).sample(&mut rand::thread_rng())
Call a function f on every node of binary tree bt, in depth-first infix order
fn depthFirstTraverse<T>(bt: &mut BiTree<T>, f: fn(&mut BiTree<T>)) {
    if let Some(left) = &mut bt.left {
        depthFirstTraverse(left, f);
    if let Some(right) = &mut bt.right {
        depthFirstTraverse(right, f);
The structure must be recursive. A node may have zero or more children. A node has access to its children nodes, but not to its parent.
struct Node<T> {
  value: T,
  children: Vec<Node<T>>,
Call a function f on every node of a tree, in depth-first prefix order
pub struct Tree<V> {
    children: Vec<Tree<V>>,
    value: V

impl<V> Tree<V> {
    pub fn dfs<F: Fn(&V)>(&self, f: F) {
    fn dfs_helper<F: Fn(&V)>(&self, f: &F) {
        for child in &self.children {
    // ...
Reverse the order of the elements of the list x.
This may reverse "in-place" and destroy the original ordering.
let y: Vec<_> = x.into_iter().rev().collect();
Alternative implementation:
Implement a function search which looks for item x in a 2D matrix m.
Return indices i, j of the matching cell.
Think of the most idiomatic way in the language to return the two values at the same time.
fn search<T: Eq>(m: &Vec<Vec<T>>, x: &T) -> Option<(usize, usize)> {
    for (i, row) in m.iter().enumerate() {
        for (j, column) in row.iter().enumerate() {
            if *column == *x {
                return Some((i, j));

Swap the values of the variables a and b
std::mem::swap(&mut a, &mut b);
Alternative implementation:
let (a, b) = (b, a);
Extract the integer value i from its string representation s (in radix 10)
let i = s.parse::<i32>().unwrap();
Alternative implementation:
let i: i32 = s.parse().unwrap_or(0);
Alternative implementation:
let i = match s.parse::<i32>() {
  Ok(i) => i,
  Err(_e) => -1,
Given a real number x, create its string representation s with 2 decimal digits following the dot.
let s = format!("{:.2}", x);
Declare a new string s and initialize it with the literal value "ネコ" (which means "cat" in japanese)
let s = "ネコ";
Share the string value "Alan" with an existing running process which will then display "Hello, Alan"
let (send, recv) = channel();

thread::spawn(move || {
    loop {
        let msg = recv.recv().unwrap();
        println!("Hello, {:?}", msg);

Declare and initialize a matrix x having m rows and n columns, containing real numbers.
let mut x = vec![vec![0.0f64; N]; M];
Alternative implementation:
let mut x = [[0.0; N] ; M];
Declare and initialize a 3D array x, having dimensions boundaries m, n, p, and containing real numbers.
let x = vec![vec![vec![0.0f64; p]; n]; m];
Alternative implementation:
let x = [[[0.0f64; P]; N]; M];
Sort the elements of the list (or array-like collection) items in ascending order of x.p, where p is a field of the type Item of the objects in items.
items.sort_by(|a,b| a.p.cmp(&b.p));
Alternative implementation:
items.sort_by_key(|x| x.p);
Remove i-th item from list items.
This will alter the original list or return a new list, depending on which is more idiomatic.
Note that in most languages, the smallest valid value for i is 0.
Launch the concurrent execution of procedure f with parameter i from 1 to 1000.
Tasks are independent and f(i) doesn't return any value.
Tasks need not run all at the same time, so you may use a pool.
let threads: Vec<_> = (0..1000).map(|i| {
	thread::spawn(move || f(i))

for thread in threads {
Alternative implementation:
Create the recursive function f which returns the factorial of the non-negative integer i, calculated from f(i-1)
fn f(n: u32) -> u32 {
    if n < 2 {
    } else {
        n * f(n - 1)
Alternative implementation:
fn factorial(num: u64) -> u64 {
    match num {
        0 | 1 => 1,
        _ => factorial(num - 1) * num,
Create function exp which calculates (fast) the value x power n.
x and n are non-negative integers.
fn exp(x: u64, n: u64) -> u64 {
    match n {
        0 => 1,
        1 => x,
        i if i % 2 == 0 => exp(x * x, n / 2),
        _ => x * exp(x * x, (n - 1) / 2),
Alternative implementation:
fn exp(x: u64, n: u32) -> u64 {
Assign to the variable x the new value f(x), making sure that no other thread may modify x between the read and the write.
let mut x = x.lock().unwrap();
*x = f(x);
Declare and initialize a set x containing unique objects of type T.
let x: HashSet<T> = HashSet::new();
Implement a function compose (A -> C) with parameters f (A -> B) and g (B -> C), which returns the composition function g ∘ f
fn compose<'a, A, B, C, G, F>(f: F, g: G) -> Box<Fn(A) -> C + 'a>
	where F: 'a + Fn(A) -> B, G: 'a + Fn(B) -> C
	Box::new(move |x| g(f(x)))
Alternative implementation:
fn compose<A, B, C>(f: impl Fn(A) -> B, g: impl Fn(B) -> C) -> impl Fn(A) -> C {
    move |x| g(f(x))
Implement a function compose which returns composition function g ∘ f for any functions f and g having exactly 1 parameter.
fn compose<'a, A, B, C, G, F>(f: F, g: G) -> Box<Fn(A) -> C + 'a>
	where F: 'a + Fn(A) -> B, G: 'a + Fn(B) -> C
	Box::new(move |x| g(f(x)))
Alternative implementation:
fn compose<A, B, C>(f: impl Fn(A) -> B, g: impl Fn(B) -> C) -> impl Fn(A) -> C {
    move |x| g(f(x))
Transform a function that takes multiple arguments into a function for which some of the arguments are preset.
fn add(a: u32, b: u32) -> u32 {
    a + b

let add5 = move |x| add(5, x);
Find substring t consisting in characters i (included) to j (excluded) of string s.
Character indices start at 0 unless specified otherwise.
Make sure that multibyte characters are properly handled.
let t = s.graphemes(true).skip(i).take(j - i).collect::<String>();
Alternative implementation:
let t = s.substring(i, j);
Alternative implementation:
let mut iter = s.grapheme_indices(true);
let i_idx = iter.nth(i).map(|x|x.0).unwrap_or(0);
let j_idx = iter.nth(j-i).map(|x|x.0).unwrap_or(0);
let t = s[i_idx..j_idx];
Set the boolean ok to true if the string word is contained in string s as a substring, or to false otherwise.
let ok = s.contains(word);
Create string t containing the same characters as string s, in reverse order.
Original string s must remain unaltered. Each character must be handled correctly regardless its number of bytes in memory.
let t = s.chars().rev().collect::<String>();
Alternative implementation:
let t: String = s.chars().rev().collect();
Print each item v of list a which is not contained in list b.
For this, write an outer loop to iterate on a and an inner loop to iterate on b.
'outer: for va in &a {
    for vb in &b {
        if va == vb {
            continue 'outer;
    println!("{}", va);
Look for a negative value v in 2D integer matrix m. Print it and stop searching.
'outer: for v in m {
    'inner: for i in v {
        if i < 0 {
            println!("Found {}", i);
            break 'outer;
Insert the element x at position i in the list s. Further elements must be shifted to the right.
s.insert(i, x);
Sleep for 5 seconds in current thread, before proceeding with the next instructions.
Create the string t consisting of the 5 first characters of the string s.
Make sure that multibyte characters are properly handled.
let t = s.char_indices().nth(5).map_or(s, |(i, _)| &s[..i]);
Alternative implementation:
let t = s.chars().take(5).collect::<String>();
Create string t consisting in the 5 last characters of string s.
Make sure that multibyte characters are properly handled.
let last5ch = s.chars().count() - 5;
let t: String = s.chars().skip(last5ch).collect();
Alternative implementation:
let s = "a̐éö̲\r\n";
let t = s.grapheme_indices(true).rev().nth(5).map_or(s, |(i,_)|&s[i..]);
Assign to variable s a string literal consisting in several lines of text, including newlines.
let s = "line 1
line 2
line 3";
Alternative implementation:
let s = r#"Huey
Build list chunks consisting in substrings of the string s, separated by one or more space characters.
let chunks: Vec<_> = s.split_whitespace().collect();
Alternative implementation:
let chunks: Vec<_> = s.split_ascii_whitespace().collect();
Alternative implementation:
let chunks: Vec<_> = s.split(' ').collect();
Write a loop that has no end clause.
loop {
	// Do something
Determine whether the map m contains an entry for the key k
Determine whether the map m contains an entry with the value v, for some key.
let does_contain = m.values().any(|&val| *val == v);
Concatenate elements of string list x joined by the separator ", " to create a single string y.
let y = x.join(", ");
Calculate the sum s of the integer list or array x.
Alternative implementation:
let s = x.iter().sum::<i32>();
Create the string representation s (in radix 10) of the integer value i.
let s = i.to_string();
Alternative implementation:
let s = format!("{}", i);
Fork-join : launch the concurrent execution of procedure f with parameter i from 1 to 1000.
Tasks are independent and f(i) doesn't return any value.
Tasks need not run all at the same time, so you may use a pool.
Wait for the completion of the 1000 tasks and then print "Finished".
let threads: Vec<_> = (0..1000).map(|i| thread::spawn(move || f(i))).collect();

for t in threads {
Create the list y containing the items from the list x that satisfy the predicate p. Respect the original ordering. Don't modify x in-place.
let y: Vec<_> = x.iter().filter(p).collect();
Create the string lines from the content of the file with filename f.
let mut file = File::open(f)?;
let mut lines = String::new();
file.read_to_string(&mut lines)?;
Alternative implementation:
let lines = fs::read_to_string(f).expect("Can't read file.");
Print the message "x is negative" to standard error (stderr), with integer x value substitution (e.g. "-2 is negative").
eprintln!("{} is negative", x);
Assign to x the string value of the first command line parameter, after the program name.
let first_arg = env::args().skip(1).next();

let fallback = "".to_owned();
let x = first_arg.unwrap_or(fallback);
Alternative implementation:
let x = env::args().nth(1).unwrap_or("".to_string());
Assign to the variable d the current date/time value, in the most standard type.
let d = time::now();
Alternative implementation:
let d = SystemTime::now();
Set i to the first position of string y inside string x, if exists.

Specify if i should be regarded as a character index or as a byte index.

Explain the behavior when y is not contained in x.
let i = x.find(y);
Assign to x2 the value of string x with all occurrences of y replaced by z.
Assume occurrences of y are not overlapping.
let x2 = x.replace(&y, &z);
Assign to x the value 3^247
let a = 3.to_bigint().unwrap();
let x = num::pow(a, 247);
From the real value x in [0,1], create its percentage string representation s with one digit after decimal point. E.g. 0.15625 -> "15.6%"
let s = format!("{:.1}%", 100.0 * x);
Calculate the result z of x power n, where x is a big integer and n is a positive integer.
let z = num::pow(x, n);
Calculate binom(n, k) = n! / (k! * (n-k)!). Use an integer type able to handle huge numbers.
fn binom(n: u64, k: u64) -> BigInt {
    let mut res = BigInt::one();
    for i in 0..k {
        res = (res * (n - i).to_bigint().unwrap()) /
              (i + 1).to_bigint().unwrap();
Create an object x to store n bits (n being potentially large).
let mut x = vec![false; n];
Use seed s to initialize a random generator.

If s is constant, the generator output will be the same each time the program runs. If s is based on the current value of the system clock, the generator output will be different each time.
let s = 32;
let mut rng = StdRng::seed_from_u64(s);
Get the current datetime and provide it as a seed to a random generator. The generator sequence will be different at each run.
let d = SystemTime::now()
    .expect("Duration since UNIX_EPOCH failed");
let mut rng = StdRng::seed_from_u64(d.as_secs());
Basic implementation of the Echo program: Print all arguments except the program name, separated by space, followed by newline.
The idiom demonstrates how to skip the first argument if necessary, concatenate arguments as strings, append newline and print it to stdout.
println!("{}", env::args().skip(1).collect::<Vec<_>>().join(" "));
Alternative implementation:
println!("{}", std::env::args().skip(1).format(" "));
Create a factory named fact for any sub class of Parent and taking exactly one string str as constructor parameter.
fn fact<Parent: std::str::FromStr>(str: String, _: Parent) -> Parent where <Parent as FromStr>::Err: Debug 
    return str.parse::<Parent>().unwrap();
Compute the greatest common divisor x of big integers a and b. Use an integer type able to handle huge numbers.
let x = a.gcd(&b);
Compute the least common multiple x of big integers a and b. Use an integer type able to handle huge numbers.
let x = a.lcm(&b);
Create the string s of integer x written in base 2.

E.g. 13 -> "1101"
let s = format!("{:b}", x);
Alternative implementation:
let s = format!("{x:b}");
Declare a complex x and initialize it with value (3i - 2). Then multiply it by i.
let mut x = Complex::new(-2, 3);
x *= Complex::i();
Execute a block once, then execute it again as long as boolean condition c is true.
loop {
    if !c { break; }
Alternative implementation:
while {
} { /* EMPTY */ }
Declare the floating point number y and initialize it with the value of the integer x .
let y = x as f64;
Declare integer y and initialize it with the value of floating point number x . Ignore non-integer digits of x .
Make sure to truncate towards zero: a negative x must yield the closest greater integer (not lesser).
let y = x as i32;
Declare the integer y and initialize it with the rounded value of the floating point number x .
Ties (when the fractional part of x is exactly .5) must be rounded up (to positive infinity).
let y = x.round() as i64;
Find how many times string s contains substring t.
Specify if overlapping occurrences are counted.
let c = s.matches(t).count();
Declare regular expression r matching strings "http", "htttp", "httttp", etc.
let r = Regex::new(r"htt+p").unwrap();
Count number c of 1s in the integer i in base 2.

E.g. i=6 → c=2
let c = i.count_ones();
Write boolean function addingWillOverflow which takes two integers x, y and return true if (x+y) overflows.

An overflow may be above the max positive value, or below the min negative value.
fn adding_will_overflow(x: usize, y: usize) -> bool {
Write the boolean function multiplyWillOverflow which takes two integers x, y and returns true if (x*y) overflows.

An overflow may reach above the max positive value, or below the min negative value.
fn multiply_will_overflow(x: i64, y: i64) -> bool {
Exit immediately.
If some extra cleanup work is executed by the program runtime (not by the OS itself), describe it.
Create a new bytes buffer buf of size 1,000,000.
let buf: Vec<u8> = Vec::with_capacity(1000000);
You've detected that the integer value of argument x passed to the current function is invalid. Write the idiomatic way to abort the function execution and signal the problem.
enum CustomError { InvalidAnswer }

fn do_stuff(x: i32) -> Result<i32, CustomError> {
    if x != 42 {
    } else {
Expose a read-only integer x to the outside world while being writable inside a structure or a class Foo.
struct Foo {
    x: usize

impl Foo {
    pub fn new(x: usize) -> Self {
        Foo { x }

    pub fn x<'a>(&'a self) -> &'a usize {

    pub fn bar(&mut self) {
        self.x += 1;
Read from the file data.json and write its content into the object x.
Assume the JSON data is suitable for the type of x.
let x = ::serde_json::from_reader(File::open("data.json")?)?;
Write the contents of the object x into the file data.json.
::serde_json::to_writer(&File::create("data.json")?, &x)?
Implement the procedure control which receives one parameter f, and runs f.
fn control(f: impl Fn()) {
Print the name of the type of x. Explain if it is a static type or dynamic type.

This may not make sense in all languages.
fn type_of<T>(_: &T) -> &'static str {

println!("{}", type_of(&x));
Assign to variable x the length (number of bytes) of the local file at path.
let x = fs::metadata(path)?.len();
Alternative implementation:
let x = path.metadata()?.len();
Set the boolean b to true if string s starts with prefix prefix, false otherwise.
let b = s.starts_with(prefix);
Set boolean b to true if string s ends with string suffix, false otherwise.
let b = s.ends_with(suffix);
Convert a timestamp ts (number of seconds in epoch-time) to a date with time d. E.g. 0 -> 1970-01-01 00:00:00
let d = NaiveDateTime::from_timestamp(ts, 0);
Assign to the string x the value of the fields (year, month, day) of the date d, in format YYYY-MM-DD.
Alternative implementation:
let format = format_description!("[year]-[month]-[day]");
let x = d.format(&format).expect("Failed to format the date");
Sort elements of array-like collection items, using a comparator c.
Make an HTTP request with method GET to the URL u, then store the body of the response in the string s.
let client = Client::new();
let s = client.get(u).send().and_then(|res| res.text())?;
Alternative implementation:
let s = ureq::get(u).call().into_string()?;
Alternative implementation:
let mut response = reqwest::blocking::get(u)?;
let mut s = String::new();
response.read_to_string(&mut s)?;
Make an HTTP request with method GET to the URL u, then store the body of the response in the file result.txt. Try to save the data as it arrives if possible, without having all its content in memory at once.
let client = Client::new();
match client.get(&u).send() {
    Ok(res) => {
        let file = File::create("result.txt")?;
        ::std::io::copy(res, file)?;
    Err(e) => eprintln!("failed to send request: {}", e),
Assign to the string s the name of the currently executing program (but not its full path).
fn get_exec_name() -> Option<String> {
        .and_then(|pb| pb.file_name().map(|s| s.to_os_string()))
        .and_then(|s| s.into_string().ok())

fn main() -> () {
    let s = get_exec_name().unwrap();
    println!("{}", s);
Alternative implementation:
let s = std::env::current_exe()
    .expect("Can't get the exec path")
    .expect("Can't get the exec name")
Assign to string dir the path of the working directory.
(This is not necessarily the folder containing the executable itself)
let dir = env::current_dir().unwrap();
Assign to string dir the path of the folder containing the currently running executable.
(This is not necessarily the working directory, though.)
let dir = std::env::current_exe()?
    .expect("the current exe should exist")
    .expect("the current exe should be a file")
Set n to the number of bytes of a variable t (of type T).
let n = std::mem::size_of::<T>();
Set the boolean blank to true if the string s is empty, or null, or contains only whitespace ; false otherwise.
let blank = s.trim().is_empty();
Alternative implementation:
let blank = s.chars().all(|c| c.is_whitespace());
From current process, run program x with command-line parameters "a", "b".
let output = Command::new("x")
    .args(&["a", "b"])
    .expect("failed to execute process");
Alternative implementation:
let output = Command::new("x")
        .args(&["a", "b"])
        .expect("failed to execute process");
Alternative implementation:
let output = Command::new("x")
        .args(&["a", "b"])
        .expect("failed to execute process");
Print each key k with its value x from an associative array mymap, in ascending order of k.
for (k, x) in mymap {
    println!("({}, {})", k, x);
Print each key k with its value x from an associative array mymap, in ascending order of x.
Multiple entries may exist for the same value x.
for (k, x) in mymap.iter().sorted_by_key(|x| x.1) {
	println!("[{},{}]", k, x);
Alternative implementation:
let mut items: Vec<_> = mymap.iter().collect();
items.sort_by_key(|item| item.1);
for (k, x) in items {
    println!("[{},{}]", k, x);
Set boolean b to true if objects x and y contain the same values, recursively comparing all referenced elements in x and y.
Tell if the code correctly handles recursive types.
let b = x == y;
Set boolean b to true if date d1 is strictly before date d2 ; false otherwise.
let b = d1 < d2;
Remove all occurrences of string w from string s1, and store the result in s2.
s2 = s1.replace(w, "");
Alternative implementation:
let s2 = str::replace(s1, w, "");
Set n to the number of elements of the list x.
let n = x.len();

Create the set y from the list x.
x may contain duplicates. y is unordered and has no repeated values.
let y: HashSet<_> = x.into_iter().collect();
Remove duplicates from the list x.
Explain if the original order is preserved.
Alternative implementation:
let dedup: Vec<_> = x.iter().unique().collect();
Read an integer value from the standard input into the variable n
fn get_input() -> String {
    let mut buffer = String::new();
    std::io::stdin().read_line(&mut buffer).expect("Failed");

let n = get_input().trim().parse::<i64>().unwrap();
Alternative implementation:
let mut input = String::new();
io::stdin().read_line(&mut input).unwrap();
let n: i32 = input.trim().parse().unwrap();
Alternative implementation:
let n: i32 = std::io::stdin()
    .expect("stdin should be available")
    .expect("couldn't read from stdin")
    .expect("input was not an integer");
Alternative implementation:
let n: i32 = read!();
Listen UDP traffic on port p and read 1024 bytes into buffer b.
let mut b = [0 as u8; 1024];
let sock = UdpSocket::bind(("localhost", p)).unwrap();
sock.recv_from(&mut b).unwrap();
Create an enumerated type Suit with 4 possible values SPADES, HEARTS, DIAMONDS, CLUBS.
enum Suit {
Verify that predicate isConsistent returns true, otherwise report assertion violation.
Explain if the assertion is executed even in production environment or not.
Write the function binarySearch which returns the index of an element having the value x in the sorted array a, or -1 if no such element exists.
measure the duration t, in nanoseconds, of a call to the function foo. Print this duration.
let start = Instant::now();
let duration = start.elapsed();
println!("{}", duration);
Write a function foo that returns a string and a boolean value.
fn foo() -> (String, bool) {
    (String::from("bar"), true)
Import the source code for the function foo body from a file "foobody.txt".
fn main() {
Call a function f on every node of a tree, in breadth-first prefix order
struct Tree<V> {
    children: Vec<Tree<V>>,
    value: V

impl<V> Tree<V> {
    fn bfs(&self, f: impl Fn(&V)) {
        let mut q = VecDeque::new();

        while let Some(t) = q.pop_front() {
            for child in &t.children {
Call the function f on every vertex accessible from the vertex start, in breadth-first prefix order
struct Vertex<V> {
	value: V,
	neighbours: Vec<Weak<RefCell<Vertex<V>>>>,

// ...

fn bft(start: Rc<RefCell<Vertex<V>>>, f: impl Fn(&V)) {
	let mut q = vec![start];
	let mut i = 0;
	while i < q.len() {
	    let v = Rc::clone(&q[i]);
	    i += 1;
	    for n in &v.borrow().neighbours {
	        let n = n.upgrade().expect("Invalid neighbour");
	        if q.iter().all(|v| v.as_ptr() != n.as_ptr()) {
Call th function f on every vertex accessible from the vertex v, in depth-first prefix order
struct Vertex<V> {
	value: V,
	neighbours: Vec<Weak<RefCell<Vertex<V>>>>,

// ...

fn dft_helper(start: Rc<RefCell<Vertex<V>>>, f: &impl Fn(&V), s: &mut Vec<*const Vertex<V>>) {
	for n in &start.borrow().neighbours {
		let n = n.upgrade().expect("Invalid neighbor");
		if s.iter().all(|&p| p != n.as_ptr()) {
			Self::dft_helper(n, f, s);
Execute f1 if condition c1 is true, or else f2 if condition c2 is true, or else f3 if condition c3 is true.
Don't evaluate a condition when a previous condition was true.
if c1 { f1() } else if c2 { f2() } else if c3 { f3() }
Alternative implementation:
match true {
    _ if c1 => f1(),
    _ if c2 => f2(),
    _ if c3 => f3(),
    _ => (),
Run the procedure f, and return the duration of the execution of f.
let start = Instant::now();
let duration = start.elapsed();
Set boolean ok to true if string word is contained in string s as a substring, even if the case doesn't match, or to false otherwise.
let re = Regex::new(&format!("(?i){}", regex::escape(word))).unwrap();
let ok = re.is_match(&s);
Alternative implementation:
let re =

let ok = re.is_match(s);
Alternative implementation:
let ok = s.to_ascii_lowercase().contains(&word.to_ascii_lowercase());
Declare and initialize a new list items, containing 3 elements a, b, c.
let items = vec![a, b, c];
Remove at most 1 item from list items, having the value x.
This will alter the original list or return a new list, depending on which is more idiomatic.
If there are several occurrences of x in items, remove only one of them. If x is absent, keep items unchanged.
if let Some(i) = items.first(&x) {
Alternative implementation:
if let Some(i) = items.iter().position(|item| *item == x) {
Remove all occurrences of the value x from list items.
This will alter the original list or return a new list, depending on which is more idiomatic.
items = items.into_iter().filter(|&item| item != x).collect();
Alternative implementation:
items.retain(|&item| item != x);
Set the boolean b to true if the string s contains only characters in the range '0'..'9', false otherwise.
let chars_are_numeric: Vec<bool> = s.chars()
let b = !chars_are_numeric.contains(&false);
Alternative implementation:
let b = s.chars().all(char::is_numeric);
Alternative implementation:
let b = s.bytes().all(|c| c.is_ascii_digit());
Create a new temporary file on the filesystem.
let temp_dir = TempDir::new("prefix")?;
let temp_file = File::open(temp_dir.path().join("file_name"))?;
Create a new temporary folder on filesystem, for writing.
let tmp = TempDir::new("prefix")?;
Delete from map m the entry having key k.

Explain what happens if k is not an existing key in m.
Iterate in sequence over the elements of the list items1 then items2. For each iteration print the element.
for i in item1.iter().chain(item2.iter()) {
    print!("{} ", i);
Assign to string s the hexadecimal representation (base 16) of integer x.

E.g. 999 -> "3e7"
let s = format!("{:X}", x);
Iterate alternatively over the elements of the lists items1 and items2. For each iteration, print the element.

Explain what happens if items1 and items2 have different size.
for pair in izip!(&items1, &items2) {
    println!("{}", pair.0);
    println!("{}", pair.1);
Set boolean b to true if file at path fp exists on filesystem; false otherwise.

Beware that you should never do this and then in the next instruction assume the result is still valid, this is a race condition on any multitasking OS.
let b = std::path::Path::new(fp).exists();
Print message msg, prepended by current date and time.

Explain what behavior is idiomatic: to stdout or stderr, and what the date format is.
eprintln!("[{}] {}", humantime::format_rfc3339_seconds(std::time::SystemTime::now()), msg);
Extract floating point value f from its string representation s
let f = s.parse::<f32>().unwrap();
Alternative implementation:
let f: f32 = s.parse().unwrap();
Create string t from string s, keeping only ASCII characters
let t = s.replace(|c: char| !c.is_ascii(), "");
Alternative implementation:
let t = s.chars().filter(|c| c.is_ascii()).collect::<String>();
Read a list of integer numbers from the standard input, until EOF.
let mut string = String::new();
io::stdin().read_to_string(&mut string)?;
let result = string
    .collect::<Result<Vec<_>, _>>();
Remove the last character from the string p, if this character is a forward slash /
if p.ends_with('/') { p.pop(); }
Remove last character from string p, if this character is the file path separator of current platform.

Note that this also transforms unix root path "/" into the empty string!
let p = if ::std::path::is_separator(p.chars().last().unwrap()) {
} else {
Alternative implementation:
p = p.strip_suffix(std::path::is_separator).unwrap_or(p);
Create string s containing only the character c.
let s = c.to_string();
Create the string t as the concatenation of the string s and the integer i.
let t = format!("{}{}", s, i);
Alternative implementation:
let t = format!("{s}{i}");
Find color c, the average between colors c1, c2.

c, c1, c2 are strings of hex color codes: 7 chars, beginning with a number sign # .
Assume linear computations, ignore gamma corrections.
"Too long for text box, see online demo"
Delete from filesystem the file having path filepath.
let r = fs::remove_file(filepath);
Assign to the string s the value of the integer i in 3 decimal digits. Pad with zeros if i < 100. Keep all digits if i1000.
let s = format!("{:03}", i);
Initialize a constant planet with string value "Earth".
const PLANET: &str = "Earth";
Create a new list y from randomly picking exactly k elements from list x.

It is assumed that x has at least k elements.
Each element must have same probability to be picked.
Each element from x must be picked at most once.
Explain if the original ordering is preserved or not.
let mut rng = &mut rand::thread_rng();
let y = x.choose_multiple(&mut rng, k).cloned().collect::<Vec<_>>();
Define a Trie data structure, where entries have an associated value.
(Not all nodes are entries)
struct Trie {
    val: String,
    nodes: Vec<Trie>
Execute f32() if platform is 32-bit, or f64() if platform is 64-bit.
This can be either a compile-time condition (depending on target) or a runtime detection.
match std::mem::size_of::<&char>() {
    4 => f32(),
    8 => f64(),
    _ => {}
Alternative implementation:
#[cfg(target_pointer_width = "64")]

#[cfg(target_pointer_width = "32")]
Multiply all the elements of the list elements by a constant c
let elements = elements.into_iter().map(|x| c * x).collect::<Vec<_>>();
Alternative implementation:
elements.iter_mut().for_each(|x| *x *= c);
execute bat if b is a program option and fox if f is a program option.
if let Some(arg) = ::std::env::args().nth(1) {
    if &arg == "f" {
    } else if &arg = "b" {
    } else {
	eprintln!("invalid argument: {}", arg),
} else {
    eprintln!("missing argument");
Alternative implementation:
if let Some(arg) = ::std::env::args().nth(1) {
    match arg.as_str() {
        "f" => fox(),
        "b" => box(),
        _ => eprintln!("invalid argument: {}", arg),
} else {
    eprintln!("missing argument");
Print all the list elements, two by two, assuming list length is even.
for pair in list.chunks(2) {
    println!("({}, {})", pair[0], pair[1]);
Open the URL s in the default browser.
Set the boolean b to indicate whether the operation was successful.
webbrowser::open(s).expect("failed to open URL");
Assign to the variable x the last element of the list items.
let x = items[items.len()-1];
Alternative implementation:
let x = items.last().unwrap();
Create the list ab containing all the elements of the list a, followed by all the elements of the list b.
let ab = [a, b].concat();
Create the string t consisting of the string s with its prefix p removed (if s starts with p).
let t = s.trim_start_matches(p);
Alternative implementation:
let t = if s.starts_with(p) { &s[p.len()..] } else { s };
Alternative implementation:
let t = s.strip_prefix(p).unwrap_or(s);
Create string t consisting of string s with its suffix w removed (if s ends with w).
let t = s.trim_end_matches(w);
Alternative implementation:
let t = s.strip_suffix(w).unwrap_or(s);
Assign to the integer n the number of characters of the string s.
Make sure that multibyte characters are properly handled.
n can be different from the number of bytes of s.
let n = s.chars().count();
Set n to the number of elements stored in mymap.

This is not always equal to the map capacity.
let n = mymap.len();
Append the element x to the list s.
Insert value v for key k in map m.
m.insert(k, v);
Number will be formatted with a comma separator between every group of thousands.
println!("{}", 1000.separated_string());
Make a HTTP request with method POST to the URL u
let client = reqwest::blocking::Client::new();
let mut response ="abc").send()?;
From the array a of n bytes, build the equivalent hex string s of 2n digits.
Each byte (256 possible values) is encoded as two hexadecimal characters (16 possible values per digit).
let s = a.encode_hex::<String>();
Alternative implementation:
let mut s = String::with_capacity(2 * n);
for byte in a {
    write!(s, "{:02X}", byte)?;
Alternative implementation:
let s = HEXLOWER.encode(&a);
Alternative implementation:
fn byte_to_hex(byte: u8) -> (u8, u8) {
    static HEX_LUT: [u8; 16] = [b'0', b'1', b'2', b'3', b'4', b'5', b'6', b'7', b'8', b'9', b'a', b'b', b'c', b'd', b'e', b'f'];

    let upper = HEX_LUT[(byte >> 4) as usize];
    let lower = HEX_LUT[(byte & 0xF) as usize];
    (lower, upper)

let utf8_bytes: Vec<u8> = a.iter().copied().flat_map(|byte| {
        let (lower, upper) = byte_to_hex(byte);
        [upper, lower]
let s = unsafe { String::from_utf8_unchecked(utf8_bytes) };
From hex string s of 2n digits, build the equivalent array a of n bytes.
Each pair of hexadecimal characters (16 possible values per digit) is decoded into one byte (256 possible values).
let a: Vec<u8> = Vec::from_hex(s).expect("Invalid Hex String");
Alternative implementation:
let a: Vec<u8> = decode(s).expect("Hex string should be valid");
Alternative implementation:
let a: Vec<u8> = HEXLOWER_PERMISSIVE.decode(&s.into_bytes()).unwrap();
Construct a list L that contains all filenames that have the extension ".jpg" , ".jpeg" or ".png" in directory D and all its subdirectories.
let d = Path::new("/path/to/D");
let l: Vec<PathBuf> = d
    .filter_map(|f| f.ok())
    .filter(|f| match f.path().extension() {
        None => false,
        Some(ex) => ex == "jpg" || ex == "jpeg" || ex == "png"
    .map(|f| f.path())
Set boolean b to true if if the point with coordinates (x,y) is inside the rectangle with coordinates (x1,y1,x2,y2) , or to false otherwise.
Describe if the edges are considered to be inside the rectangle.
struct Rect {
    x1: i32,
    x2: i32,
    y1: i32,
    y2: i32,

impl Rect {
    fn contains(&self, x: i32, y: i32) -> bool {
        return self.x1 < x && x < self.x2 && self.y1 < y && y < self.y2;
Return the center c of the rectangle with coördinates(x1,y1,x2,y2)
struct Rectangle {
    x1: f64,
    y1: f64,
    x2: f64,
    y2: f64,

impl Rectangle {
    pub fn center(&self) -> (f64, f64) {
	    ((self.x1 + self.x2) / 2.0, (self.y1 + self.y2) / 2.0)
Create the list x containing the contents of the directory d.

x may contain files and subfolders.
No recursive subfolder listing.
let x = std::fs::read_dir(d).unwrap();
Alternative implementation:
let x = std::fs::read_dir(d)?.collect::<Result<Vec<_>, _>>()?;
Output the source of the program.
fn main() {
    let x = "fn main() {\n    let x = ";
    let y = "print!(\"{}{:?};\n    let y = {:?};\n    {}\", x, x, y, y)\n}\n";
    let y = {:?};
    {}", x, x, y, y)
Alternative implementation:
fn main(){print!("{},{0:?})}}","fn main(){print!(\"{},{0:?})}}\"")}
Alternative implementation:
fn main() {
    print!("{}", include_str!(""))
Assign to variable t a string representing the day, month and year of the day after the current date.
let t = chrono::Utc::now().date().succ().to_string();
Schedule the execution of f(42) in 30 seconds.
sleep(Duration::new(30, 0));
Exit a program cleanly indicating no error to OS
Perform matrix multiplication of a real matrix a with nx rows and ny columns, a real matrix b with ny rows and nz columns and assign the value to a real matrix c with nx rows and nz columns.
let c =;
Produce a new list y containing the result of the function T applied to all elements e of the list x that match the predicate P.
let y = x.iter()
Declare an external C function with the prototype

void foo(double *a, int n);

and call it, passing an array (or a list) of size 10 to a and 10 to n.

Use only standard features of your language.
extern "C" {
    /// # Safety
    /// `a` must point to an array of at least size 10
    fn foo(a: *mut libc::c_double, n: libc::c_int);

let mut a = [0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0];
let n = 10;
unsafe {
    foo(a.as_mut_ptr(), n);
Given a one-dimensional array a, check if any value is larger than x, and execute the procedure f if that is the case
if a.iter().any(|&elem| elem > x) {
Declare a real variable a with at least 20 digits; if the type does not exist, issue an error at compile time.
let a = Decimal::from_str("1234567890.123456789012345").unwrap();
Declare two two-dimensional arrays a and b of dimension n*m and m*n, respectively. Assign to b the transpose of a (i.e. the value with index interchange).
let a = DMatrix::<u8>::from_fn(n, m, |_, _| rand::thread_rng().gen());
let b = a.transpose();
Pass an array a of real numbers to the procedure (resp. function) foo. Output the size of the array, and the sum of all its elements when each element is multiplied with the array indices i and j (assuming they start from one).
fn foo(a: Vec<Vec<usize>>) {
        "Length of array: {}",

    let mut sum = 0;
    for (i, j) in izip!(&a[0], &a[1]) {
        sum += i * j

    println!("Sum of all products of indices: {}", sum);
Given an integer array a of size n, pass the first, third, fifth and seventh, ... up to the m th element to a routine foo which sets all these elements to 42.
fn foo(el: &mut i32) {
    *el = 42;
Retrieve the contents of file at path into a list of strings lines, in which each element is a line of the file.
let lines = BufReader::new(File::open(path).unwrap())
Abort program execution with error condition x (where x is an integer value)
Truncate a file F at the given file position.
let pos = f.stream_position()?;
Compute the hypotenuse h of the triangle where the sides adjacent to the square angle have lengths x and y.
fn hypot(x:f64, y:f64)-> f64 {
    let num = x.powi(2) + y.powi(2);
Alternative implementation:
let h = x.hypot(y);
Calculate n, the Euclidean norm of data (an array or list of floating point values).
fn euclidean(data: Vec<f64>) -> f64 {
    let mut n = 0.0;
    for i in data {
        n += i*i;
    return sqrt(n as f64)
let n = euclidean(data);
Calculate the sum of squares s of data, an array of floating point values.
let s = data.iter().map(|x| x.powi(2)).sum::<f32>();
Given a real number a, print the fractional part and the exponent of the internal representation of that number. For 3.14, this should print (approximately)

0.785 2
let sign = if a < 0.0 { a = -a; -1 } else { 1 };
let exponent = (a + f64::EPSILON).log2().ceil() as i32;
let fraction = a / 2.0f64.powi(exponent);
Read an environment variable with the name "FOO" and assign it to the string variable foo. If it does not exist or if the system does not support environment variables, assign a value of "none".
let foo = match env::var("FOO") {
    Ok(val) => val,
    Err(_e) => "none".to_string(),
Alternative implementation:
let foo = env::var("FOO").unwrap_or("none".to_string());
Alternative implementation:
let foo = match env::var("FOO") {
    Ok(val) => val,
    Err(_e) => "none".to_string(),
Alternative implementation:
if let Ok(tnt_root) = env::var("TNT_ROOT") {
Execute different procedures foo, bar, baz and barfl if the string str contains the name of the respective procedure. Do it in a way natural to the language.
match str {
    "foo" => foo(),
    "bar" => bar(),
    "baz" => baz(),
    "barfl" => barfl(),
    _ => {}
Allocate a list a containing n elements (n assumed to be too large for a stack) that is automatically deallocated when the program exits the scope it is declared in.
let a = vec![0; n];
Given the arrays a,b,c,d of equal length and the scalar e, calculate a = e*(a+b*c+cos(d)).
Store the results in a.
for i in 0..a.len() {
    a[i] = e * (a[i] + b[i] * c[i] + d[i].cos());
Declare a type t which contains a string s and an integer array n with variable size, and allocate a variable v of type t. Allocate v.s and v.n and set them to the values "Hello, world!" for s and [1,4,9,16,25], respectively. Deallocate v, automatically deallocating v.s and v.n (no memory leaks).
struct T {
	s: String,
	n: Vec<usize>,

fn main() {
	let v = T {
		s: "Hello, world!".into(),
		n: vec![1,4,9,16,25]
Create the folder at path on the filesystem
Alternative implementation:
Set the boolean b to true if path exists on the filesystem and is a directory; false otherwise.
let b: bool = Path::new(path).is_dir();
Compare four strings in pair-wise variations. The string comparison can be implemented with an equality test or a containment test, must be case-insensitive and must apply Unicode casefolding.
for x in strings
    .filter(|x| x[0].to_lowercase() == x[1].to_lowercase())
    println!("{:?} == {:?}", x[0], x[1])
Append extra character c at the end of string s to make sure its length is at least m.
The length is the number of characters, not the number of bytes.
let out = s.pad_to_width_with_char(m, c);
Prepend extra character c at the beginning of string s to make sure its length is at least m.
The length is the number of characters, not the number of bytes.
if let Some(columns_short) = m.checked_sub(s.width()) {
    let padding_width = c
        .filter(|n| *n > 0)
        .expect("padding character should be visible");
    // Saturate the columns_short
    let padding_needed = columns_short + padding_width - 1 / padding_width;
    let mut t = String::with_capacity(s.len() + padding_needed);
    t.extend((0..padding_needed).map(|_| c)
    s = t;
Add the extra character c at the beginning and ending of string s to make sure its length is at least m.
After the padding the original content of s should be at the center of the result.
The length is the number of characters, not the number of bytes.

E.g. with s="abcd", m=10 and c="X" the result should be "XXXabcdXXX".
let n = (m + s.len())/2;
s = format!("{s:X>n$}");
s = format!("{out:X<m$}");
Alternative implementation:
s = s.pad(m, c, Alignment::Middle, true);
Create a zip-file with filename name and add the files listed in list to that zip-file.
let path = std::path::Path::new(_name);
let file = std::fs::File::create(&path).unwrap();
let mut zip = zip::ZipWriter::new(file); zip.start_file("readme.txt", FileOptions::default())?;                                                          
zip.write_all(b"Hello, World!\n")?;
Alternative implementation:
fn zip(_name: &str, _list: Vec<&str>) -> zip::result::ZipResult<()>
    let path = std::path::Path::new(_name);
    let file = std::fs::File::create(&path).unwrap();
    let mut zip = zip::ZipWriter::new(file);
    for i in _list.iter() {
        zip.start_file(i as &str, FileOptions::default())?;
Create the list c containing all unique elements that are contained in both lists a and b.
c should not contain any duplicates, even if a and b do.
The order of c doesn't matter.
let unique_a = a.iter().collect::<HashSet<_>>();
let unique_b = b.iter().collect::<HashSet<_>>();

let c = unique_a.intersection(&unique_b).collect::<Vec<_>>();
Alternative implementation:
let set_a: HashSet<_> = a.into_iter().collect();
let set_b: HashSet<_> = b.into_iter().collect();
let c = set_a.intersection(&set_b);
Create the string t from the value of string s with each sequence of spaces replaced by a single space.

Explain if only the space characters will be replaced, or the other whitespaces as well: tabs, newlines.
let re = Regex::new(r"\s+").unwrap();
let t = re.replace_all(s, " ");
Create t consisting of 3 values having different types.

Explain if the elements of t are strongly typed or not.
let t = (2.5, "hello", -1);
Create string t from string s, keeping only digit characters 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
let t: String = s.chars().filter(|c| c.is_digit(10)).collect();
Set i to the first index in list items at which the element x can be found, or -1 if items does not contain x.
let opt_i = items.iter().position(|y| *y == x);

let i = match opt_i {
   Some(index) => index as i32,
   None => -1
Alternative implementation:
let i = items.iter().position(|y| *y == x).map_or(-1, |n| n as i32);
Loop through list items checking a condition. Do something else if no matches are found.

A typical use case is looping through a series of containers looking for one that matches a condition. If found, an item is inserted; otherwise, a new container is created.

These are mostly used as an inner nested loop, and in a location where refactoring inner logic into a separate function reduces clarity.
let mut found = false;
for item in items {
    if item == &"baz" {
        println!("found it");
        found = true;
if !found {
    println!("never found it");
Alternative implementation:
if let None = items.iter().find(|&&item| item == "rockstar programmer") {
Alternative implementation:
    .find(|&&item| item == "rockstar programmer")
    .or_else(|| {
        Some(&"rockstar programmer")
Alternative implementation:
if 'search: loop {
    for i in items {
        if i == &"qux" {
            println!("found it");
            break 'search false;
    break 'search true
} {
    println!("not found!");
Alternative implementation:
'label: {
	for &item in items {
		if item == "baz" {
			break 'label;
	println!("not found");
Insert the element x at the beginning of the list items.
Declare an optional integer argument x to procedure f, printing out "Present" and its value if it is present, "Not present" otherwise
fn f(x: Option<()>) {
    match x {
        Some(x) => println!("Present {}", x),
        None => println!("Not present"),
Remove the last element from the list items.
Create the new list y containing the same elements as the list x.

Subsequent modifications of y must not affect x (except for the contents referenced by the elements themselves if they contain pointers).
let y = x.clone();
Copy the file at path src to dst.
fs::copy(src, dst).unwrap();
Cancel an ongoing processing p if it has not finished after 5s.
timeout(Duration::from_secs(5), p()).await;
Set b to true if the byte sequence s consists entirely of valid UTF-8 character code points, false otherwise.
let b = std::str::from_utf8(&bytes).is_ok();
Print "verbose is true" if the flag -v was passed to the program command line, "verbose is false" otherwise.
let matches = App::new("My Program")
if matches.is_present("verbose") {
    println!("verbose is true")
} else {
    println!("verbose is false")
Assign to the string s the standard base64 encoding of the byte array data, as specified by RFC 4648.
let s = base64::encode(data);
Assign to byte array data the bytes represented by the base64 string s, as specified by RFC 4648.
let bytes = base64::decode(s).unwrap();
Assign to c the result of (a xor b)
let c = a ^ b;
Write in a new byte array c the xor result of byte arrays a and b.

a and b have the same size.
let c: Vec<_> = a.iter().zip(b).map(|(x, y)| x ^ y).collect();
Assign to string x the first word of string s consisting of exactly 3 digits, or the empty string if no such match exists.

A word containing more digits, or 3 digits as a substring fragment, must not match.
let re = Regex::new(r"\b\d\d\d\b").expect("failed to compile regex");
let x = re.find(s).map(|x| x.as_str()).unwrap_or("");
Lists a and b have the same length. Apply the same permutation to a and b to have them sorted based on the values of a.
let mut tmp: Vec<_> = a.iter().zip(b).collect();
tmp.as_mut_slice().sort_by_key(|(&x, _y)| x);
let (aa, bb): (Vec<i32>, Vec<i32>) = tmp.into_iter().unzip();
Explicitly decrease the priority of the current process, so that other execution threads have a better chance to execute now. Then resume normal execution and call the function busywork.
Call a function f on each element e of a set x.
for item in &x {
Print the contents of the list or array a on the standard output.
println!("{:?}", a)
Print the contents of the map m to the standard output: keys and values.
println!("{:?}", m);
Print the value of object x having custom type T, for log or debug.
println!("{:?}", x);
Set c to the number of distinct elements in the list items.
let c = items.iter().unique().count();
Remove all the elements from list x that don't satisfy the predicate p, without allocating a new list.
Keep all the elements that do satisfy p.

For languages that don't have mutable lists, refer to idiom #57 instead.
let mut j = 0;
for i in 0..x.len() {
    if p(x[i]) {
        x[j] = x[i];
        j += 1;
Alternative implementation:
Construct the "double precision" (64-bit) floating point number d from the mantissa m, the exponent e and the sign flag s (true means the sign is negative).
let d = if s { -1.0 } else { 1.0 } * m as f64 * 2.0f64.powf(e as f64);
Define variables a, b and c in a concise way.
Explain if they need to have the same type.
let (a, b, c) = (42, "hello", 5.0);
Choose a value x from map m.
m must not be empty. Ignore the keys.
let mut rng = rand::thread_rng();
let x = m.values().choose(&mut rng).expect("m is empty");
Extract integer value i from its binary string representation s (in radix 2)
E.g. "1101" -> 13
let i = i32::from_str_radix(s, 2).expect("Not a binary number!");
Assign to the variable x the string value "a" if calling the function condition returns true, or the value "b" otherwise.
x = if condition() { "a" } else { "b" };
Print the stack frames of the current execution thread of the program.
let bt = Backtrace::new();
println!("{:?}", bt);
Replace all exact occurrences of "foo" with "bar" in the string list x
for v in &mut x {
    if *v == "foo" {
        *v = "bar";
Print the values of the set x to the standard output.
The order of the elements is irrelevant and is not required to remain the same next time.
println!("{:?}", x);
Print the numbers 5, 4, ..., 0 (included), one line per number.
(0..=5).rev().for_each(|i| println!("{}", i));
Alternative implementation:
for i in (0..=5).rev() {
    println!("{}", i);
Print each index i and value x from the list items, from the last down to the first.
for (i, item) in items.iter().enumerate().rev() {
    println!("{} = {}", i, *item);
Alternative implementation:
  for (i, x) in items.iter().rev().enumerate() {
    println!("{i} = {x}");
Convert the string values from list a into a list of integers b.
let b: Vec<i64> = a.iter().map(|x| x.parse::<i64>().unwrap()).collect();
Alternative implementation:
let b: Vec<i32> = a.iter().flat_map(|s| s.parse().ok()).collect();
Build the list parts consisting of substrings of the input string s, separated by any of the characters ',' (comma), '-' (dash), '_' (underscore).
let parts: Vec<_> = s.split(&[',', '-', '_'][..]).collect();
Declare a new list items of string elements, containing zero elements
let items: Vec<String> = vec![];
Assign to the string x the value of fields (hours, minutes, seconds) of the date d, in format HH:MM:SS.
let format = format_description!("[hour]:[minute]:[second]");
let x = d.format(&format).expect("Failed to format the time");
Assign to t the number of trailing 0 bits in the binary representation of the integer n.

E.g. for n=112, n is 1110000 in base 2 ⇒ t=4
let t = n.trailing_zeros();
Write two functions log2d and log2u, which calculate the binary logarithm of their argument n rounded down and up, respectively. n is assumed to be positive. Print the result of these functions for numbers from 1 to 12.
fn log2d(n: f64) -> f64 {

fn log2u(n: f64) -> f64 {

fn main() {
    for n in 1..=12 {
        let f = f64::from(n);
        println!("{} {} {}", n, log2d(f), log2u(f));
Pass a two-dimensional integer array a to a procedure foo and print the size of the array in each dimension. Do not pass the bounds manually. Call the procedure with a two-dimensional array.
fn foo(matrix: &[Vec<i32>]) {
    let iter = matrix.iter();
    let (vertical, _) = iter.size_hint();
    let horizontal = iter
        .expect("empty array!")
    println!("{horizontal} by {vertical}");

fn main() {
    let matrix = vec![
        vec![1, 2, 3],
        vec![4, 5, 6],
Alternative implementation:
fn foo<const X: usize, const Y: usize>(_: [[i32;X];Y]) {
    println!("{} {}", Y, X);

let a = [
    [1, 2, 3],
    [4, 5, 6],
Calculate the parity p of the integer variable i : 0 if it contains an even number of bits set, 1 if it contains an odd number of bits set.
let i = 42i32;
let p = i.count_ones() % 2;
Assign to the string s the value of the string v repeated n times, and write it out.

E.g. v="abc", n=5 ⇒ s="abcabcabcabcabc"
let s = v.repeat(n);
Declare an argument x to a procedure foo that can be of any type. If the type of the argument is a string, print it, otherwise print "Nothing."

Test by passing "Hello, world!" and 42 to the procedure.
fn foo(x: &dyn Any) {
    if let Some(s) = x.downcast_ref::<String>() {
        println!("{}", s);
    } else {

fn main() {
    foo(&"Hello, world!".to_owned());
Define a type vector containing three floating point numbers x, y, and z. Write a user-defined operator x that calculates the cross product of two vectors a and b.
struct Vector {
    x: f32,
    y: f32,
    z: f32,

impl Mul for Vector {
    type Output = Self;

    fn mul(self, rhs: Self) -> Self {
        Self {
            x: self.y * rhs.z - self.z * rhs.y,
            y: self.z * rhs.x - self.x * rhs.z,
            z: self.x * rhs.y - self.y * rhs.x,
Given the enumerated type t with 3 possible values: bike, car, horse.
Set the enum value e to one of the allowed values of t.
Set the string s to hold the string representation of e (so, not the ordinal value).
Print s.
let e = t::bike;
let s = format!("{:?}", e);

println!("{}", s);
If a variable x passed to procedure tst is of type foo, print "Same type." If it is of a type that extends foo, print "Extends type." If it is neither, print "Not related."
fn type_of<T>(_: &T) -> &str {

if type_of(&x) == type_of(&foo) {
    println!("x & foo -> same type");
} else {
    println!("x & foo -> not related");
Fizz buzz is a children's counting game, and a trivial programming task used to affirm that a programmer knows the basics of a language: loops, conditions and I/O.

The typical fizz buzz game is to count from 1 to 100, saying each number in turn. When the number is divisible by 3, instead say "Fizz". When the number is divisible by 5, instead say "Buzz". When the number is divisible by both 3 and 5, say "FizzBuzz"
for i in 1..101 {
    match i {
        i if (i % 15) == 0 => println!("FizzBuzz"),
        i if (i % 3) == 0 => println!("Fizz"),
        i if (i % 5) == 0 => println!("Buzz"),
        _ => println!("{i}"),
Set the boolean b to true if the directory at filepath p is empty (i.e. doesn't contain any other files and directories)
let b = fs::read_dir(p).unwrap().count() == 0;
Create the string t from the string s, removing all the spaces, newlines, tabulations, etc.
let t: String = s.chars().filter(|c| !c.is_whitespace()).collect();
From the string s consisting of 8n binary digit characters ('0' or '1'), build the equivalent array a of n bytes.
Each chunk of 8 binary digits (2 possible values per digit) is decoded into one byte (256 possible values).
let a: Vec<u8> = s.as_bytes()
    .map(|chunk| unsafe {
        let chunk_str = std::str::from_utf8_unchecked(chunk);
        u8::from_str_radix(chunk_str, 2).unwrap_unchecked()
Insert an element e into the set x.
Remove the element e from the set x.

Explains what happens if e was already absent from x.
Alternative implementation:
Read one line into the string line.

Explain what happens if EOF is reached.
let mut buffer = String::new();
let mut stdin = io::stdin();
stdin.read_line(&mut buffer).unwrap();
Read all the lines (until EOF) into the list of strings lines.
let lines = std::io::stdin().lock().lines().map(|x| x.unwrap()).collect::<Vec<String>>();
Remove all the elements from the map m that don't satisfy the predicate p.
Keep all the elements that do satisfy p.

Explain if the filtering happens in-place, i.e. if m is reused or if a new map is created.
m.retain(|_, &mut v| p(v));
You have a Point with integer coordinates x and y. Create a map m with key type Point (or equivalent) and value type string. Insert "Hello" at position (42, 5).
let mut map: HashMap<Point, String> = HashMap::new();
map.insert(Point { x: 42, y: 5 }, "Hello".into());
Build the list parts consisting of substrings of input string s, separated by the string sep.
let parts = s.split(sep);
Alternative implementation:
let parts = s.split(sep).collect::<Vec<&str>>();
Alternative implementation:
let parts: Vec<&str> = s.split(sep).collect();
Create a new list a (or array, or slice) of size n, where all elements are integers initialized with the value 0.
let a = vec![0; n];
Given two floating point variables a and b, set a to a to a quiet NaN and b to a signalling NaN. Use standard features of the language only, without invoking undefined behavior.
let a: f64 = f64::NAN;