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Go Rust
1
Print Hello World
Print a literal string on standard output 
fmt.Println("Hello World")
 
println!("Hello World");
2
Print Hello 10 times
Loop to execute some code a constant number of times 
for i := 0; i < 10; i++ {
	fmt.Println("Hello")
}
Alternative implementation:
fmt.Println(strings.Repeat("Hello\n", 10))
Alternative implementation:
for range 10 {
	fmt.Println("Hello")
}

for _ in 0..10 { println!("Hello"); }
Alternative implementation:
print!("{}", "Hello\n".repeat(10));
3
Create a procedure
Like a function which doesn't return any value, thus has only side effects (e.g. Print to standard output) 
func finish(name string) {
  fmt.Println("My job here is done. Good bye " + name)
}
Alternative implementation:
finish := func(name string) {
	fmt.Println("My job here is done. Good bye " + name)
}
 
fn finish(name: &str) {
    println!("My job here is done. Goodbye {}", name);
}
4
Create a function
Create a function which returns the square of an integer 
func square(x int) int {
  return x*x
}
 
fn square(x : u32) -> u32 { x * x }
5
Create a 2D Point data structure
Declare a container type for two floating-point numbers x and y 
type Point struct {
    x, y float64
}
 
struct Point {
    x: f64,
    y: f64,
}
Alternative implementation:
struct Point(f64, f64);
6
Iterate over list values
Do something with each item x of the list (or array) items, regardless indexes. 
for _, x := range items {
    doSomething(x)
}
 
for x in items {
	do_something(x);
}
Alternative implementation:
items.into_iter().for_each(|x| do_something(x));
7
Iterate over list indexes and values
Print each index i with its value x from an array-like collection items 
for i, x := range items {
    fmt.Printf("Item %d = %v \n", i, x)
}
 
for (i, x) in items.iter().enumerate() {
    println!("Item {} = {}", i, x);
}
Alternative implementation:
items.iter().enumerate().for_each(|(i, x)| {
    println!("Item {} = {}", i, x);
})
8
Create a map (associative array)
Create a new map object x, and provide some (key, value) pairs as initial content. 
x := map[string]int {"one": 1, "two": 2}
 
let mut x = BTreeMap::new();
x.insert("one", 1);
x.insert("two", 2);
Alternative implementation:
let x: HashMap<&str, i32> = [
    ("one", 1),
    ("two", 2),
].into_iter().collect();
9
Create a Binary Tree data structure
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. 
type BinTree struct {
	Label       valueType
	Left, Right *BinTree
}
Alternative implementation:
type BinTree[L any] struct {
	Label       L
	Left, Right *BinTree[L]
}
 
struct BinTree<T> {
    value: T,
    left: Option<Box<BinTree<T>>>,
    right: Option<Box<BinTree<T>>>,
}
10
Shuffle a list
Generate a random permutation of the elements of list x 
for i := range x {
	j := rand.Intn(i + 1)
	x[i], x[j] = x[j], x[i]
}
Alternative implementation:
y := make([]T, len(x))
perm := rand.Perm(len(x))
for i, v := range perm {
	y[v] = x[i]
}
Alternative implementation:
rand.Shuffle(len(x), func(i, j int) {
	x[i], x[j] = x[j], x[i]
})
Alternative implementation:
for i := len(x) - 1; i > 0; i-- {
	j := rand.Intn(i + 1)
	x[i], x[j] = x[j], x[i]
}
Alternative implementation:
func shuffle[T any](x []T) {
	rand.Shuffle(len(x), func(i, j int) {
		x[i], x[j] = x[j], x[i]
	})
}
 
let mut rng = StdRng::new().unwrap();
rng.shuffle(&mut x);
Alternative implementation:
let mut rng = thread_rng();
x.shuffle(&mut rng);
Alternative implementation:
pub fn shuffle<T>(vec: &mut [T]) {
    let n = vec.len();
    for i in 0..(n - 1) {
        let j = rand() % (n - i) + i;
        vec.swap(i, j);
    }
}

pub fn rand() -> usize {
    RandomState::new().build_hasher().finish() as usize
}
11
Pick a random element from a list
The list x must be non-empty. 
x[rand.Intn(len(x))]
Alternative implementation:
func pickT(x []T) T {
	return x[rand.Intn(len(x))]
}
Alternative implementation:
func pick[T any](x []T) T {
	return x[rand.Intn(len(x))]
}
 
x[rand::thread_rng().gen_range(0..x.len())]
Alternative implementation:
let mut rng = rand::thread_rng();
let choice = x.choose(&mut rng).unwrap();
12
Check if list contains a value
Check if the list contains the value x.
list is an iterable finite container. 
func Contains(list []T, x T) bool {
	for _, item := range list {
		if item == x {
			return true
		}
	}
	return false
}
Alternative implementation:
slices.Contains(list, x)
 
list.contains(&x);
Alternative implementation:
list.iter().any(|v| v == &x)
Alternative implementation:
(&list).into_iter().any(|v| v == &x)
Alternative implementation:
list.binary_search(&x).is_ok()
13
Iterate over map keys and values
Access each key k with its value x from an associative array mymap, and print them. 
for k, x := range mymap {
  fmt.Println("Key =", k, ", Value =", x)
}
 
for (k, x) in &mymap {
    println!("Key={key}, Value={val}", key=k, val=x);
}
14
Pick uniformly a random floating point number in [a..b)
Pick a random number greater than or equals to a, strictly inferior to b. Precondition : a < b. 
func pick(a, b  float64)  float64 {
	return a + (rand.Float64() * (b-a))
}
 
thread_rng().gen_range(a..b);
15
Pick uniformly a random integer in [a..b]
Pick a random integer greater than or equals to a, inferior or equals to b. Precondition : a < b. 
func pick(a,b int) int {
	return a + rand.Intn(b-a+1)
}
Alternative implementation:
func pick(a, b int) int {
	return a + rand.IntN(b-a+1)
}
 
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())
16
Depth-first traversal of a binary tree
Call a function f on every node of binary tree bt, in depth-first infix order 
func (bt *BinTree) Dfs(f func(*BinTree)) {
	if bt == nil {
		return
	}
	bt.Left.Dfs(f)
	f(bt)
	bt.Right.Dfs(f)
}
Alternative implementation:
func (bt *BinTree[L]) Dfs(f func(*BinTree[L])) {
	if bt == nil {
		return
	}
	bt.Left.Dfs(f)
	f(bt)
	bt.Right.Dfs(f)
}
 
fn depthFirstTraverse<T>(bt: &mut BiTree<T>, f: fn(&mut BiTree<T>)) {
    if let Some(left) = &mut bt.left {
        depthFirstTraverse(left, f);
    }
    
    f(bt);
    
    if let Some(right) = &mut bt.right {
        depthFirstTraverse(right, f);
    }
}
17
Create a Tree data structure
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. 
type Tree struct {
	Key keyType
	Deco valueType
	Children []*Tree
}
Alternative implementation:
type Tree[L any] struct {
	Label    L
	Children []*Tree[L]
}
 
struct Node<T> {
  value: T,
  children: Vec<Node<T>>,
}
18
Depth-first traversal of a tree
Call a function f on every node of a tree, in depth-first prefix order 
func (t *Tree) Dfs(f func(*Tree)) {
	if t == nil {
		return
	}
	f(t)
	for _, child := range t.Children {
		child.Dfs(f)
	}
}
Alternative implementation:
func (t *Tree[L]) Dfs(f func(*Tree[L])) {
	if t == nil {
		return
	}
	f(t)
	for _, child := range t.Children {
		child.Dfs(f)
	}
}
 
pub struct Tree<V> {
    children: Vec<Tree<V>>,
    value: V
}

impl<V> Tree<V> {
    pub fn dfs<F: Fn(&V)>(&self, f: F) {
        self.dfs_helper(&f);
    }
    fn dfs_helper<F: Fn(&V)>(&self, f: &F) {
        (f)(&self.value);
        for child in &self.children {
            child.dfs_helper(f)
        }
    }
    // ...
}
19
Reverse a list
Reverse the order of the elements of the list x.
This may reverse "in-place" and destroy the original ordering. 
for i, j := 0, len(x)-1; i < j; i, j = i+1, j-1 {
	x[i], x[j] = x[j], x[i]
}
Alternative implementation:
func reverse[T any](x []T) {
	for i, j := 0, len(x)-1; i < j; i, j = i+1, j-1 {
		x[i], x[j] = x[j], x[i]
	}
}
Alternative implementation:
slices.Reverse(x)
 
let y: Vec<_> = x.into_iter().rev().collect();
Alternative implementation:
x.reverse();
20
Return two values
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. 
func search(m [][]int, x int) (bool, int, int) {
	for i := range m {
		for j, v := range m[i] {
			if v == x {
				return true, i, j
			}
		}
	}
	return false, 0, 0
}
 
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));
            }
        }
    }

    None
}
21
Swap values
Swap the values of the variables a and b
 
a, b = b, a
 
std::mem::swap(&mut a, &mut b);
Alternative implementation:
let (a, b) = (b, a);
22
Convert string to integer
Extract the integer value i from its string representation s (in radix 10) 
i, err  := strconv.Atoi(s)
Alternative implementation:
i, err := strconv.ParseInt(s, 10, 0)
 
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,
};
23
Convert real number to string with 2 decimal places
Given a real number x, create its string representation s with 2 decimal digits following the dot. 
s := fmt.Sprintf("%.2f", x)
 
let s = format!("{:.2}", x);
24
Assign to string the japanese word ネコ
Declare a new string s and initialize it with the literal value "ネコ" (which means "cat" in japanese) 
s := "ネコ"
 
let s = "ネコ";
25
Send a value to another thread
Share the string value "Alan" with an existing running process which will then display "Hello, Alan" 
go func() {
	v := <-ch
	fmt.Printf("Hello, %v\n", v)
}()

ch <- "Alan"
 
let (send, recv) = channel();

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

send.send("Alan").unwrap();
26
Create a 2-dimensional array
Declare and initialize a matrix x having m rows and n columns, containing real numbers. 
const m, n = 3, 4
var x [m][n]float64
Alternative implementation:
func make2D(m, n int) [][]float64 {
	buf := make([]float64, m*n)

	x := make([][]float64, m)
	for i := range x {
		x[i] = buf[:n:n]
		buf = buf[n:]
	}
	return x
}
Alternative implementation:
func make2D[T any](m, n int) [][]T {
	buf := make([]T, m*n)

	x := make([][]T, m)
	for i := range x {
		x[i] = buf[:n:n]
		buf = buf[n:]
	}
	return x
}
 
let mut x = vec![vec![0.0f64; N]; M];
Alternative implementation:
let mut x = [[0.0; N] ; M];
27
Create a 3-dimensional array
Declare and initialize a 3D array x, having dimensions boundaries m, n, p, and containing real numbers. 
const m, n, p = 2, 2, 3
var x [m][n][p]float64
Alternative implementation:
func make3D(m, n, p int) [][][]float64 {
	buf := make([]float64, m*n*p)

	x := make([][][]float64, m)
	for i := range x {
		x[i] = make([][]float64, n)
		for j := range x[i] {
			x[i][j] = buf[:p:p]
			buf = buf[p:]
		}
	}
	return x
}
Alternative implementation:
func make3D[T any](m, n, p int) [][][]T {
	buf := make([]T, m*n*p)

	x := make([][][]T, m)
	for i := range x {
		x[i] = make([][]T, n)
		for j := range x[i] {
			x[i][j] = buf[:p:p]
			buf = buf[p:]
		}
	}
	return x
}
 
let x = vec![vec![vec![0.0f64; p]; n]; m];
Alternative implementation:
let x = [[[0.0f64; P]; N]; M];
28
Sort by a property
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. 
type ItemPSorter []Item
func (s ItemPSorter) Len() int{ return len(s) }
func (s ItemPSorter) Less(i,j int) bool{ return s[i].p<s[j].p }
func (s ItemPSorter) Swap(i,j int) { s[i],s[j] = s[j],s[i] }

func sortItems(items []Item){
	sorter := ItemPSorter(items)
	sort.Sort(sorter)
}
Alternative implementation:
less := func(i, j int) bool {
	return items[i].p < items[j].p
}
sort.Slice(items, less)
Alternative implementation:
compare := func(a, b Item) int {
	return cmp.Compare(a.p, b.p)
}
slices.SortFunc(items, compare)
 
items.sort_by(|a,b| a.p.cmp(&b.p));
Alternative implementation:
items.sort_by_key(|x| x.p);
29
Remove item from list, by its index
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. 
items = append(items[:i], items[i+1:]...)
Alternative implementation:
copy(items[i:], items[i+1:])
items[len(items)-1] = nil
items = items[:len(items)-1]
Alternative implementation:
items = slices.Delete(items, i, i+1)
 
items.remove(i)
30
Parallelize execution of 1000 independent tasks
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. 
wg := sync.WaitGroup{}
wg.Add(1000)
for i := 1; i <= 1000; i++ {
	go func(j int) {
          f(j)
          wg.Done()
        }(i)
}
wg.Wait()
 
let threads: Vec<_> = (0..1000).map(|i| {
	thread::spawn(move || f(i))
}).collect();

for thread in threads {
	thread.join();
}
Alternative implementation:
(0..1000).into_par_iter().for_each(f);
31
Recursive factorial (simple)
Create the recursive function f which returns the factorial of the non-negative integer i, calculated from f(i-1) 
func f(i int) int {
  if i == 0 {
    return 1
  }
  return i * f(i-1)
}
 
fn f(n: u32) -> u32 {
    if n < 2 {
        1
    } else {
        n * f(n - 1)
    }
}
Alternative implementation:
fn factorial(num: u64) -> u64 {
    match num {
        0 | 1 => 1,
        _ => factorial(num - 1) * num,
    }
}
32
Integer exponentiation by squaring
Create function exp which calculates (fast) the value x power n.
x and n are non-negative integers. 
func exp(x, n int) int {
	switch {
	case n == 0:
		return 1
	case n == 1:
		return x
	case n%2 == 0:
		return exp(x*x, n/2)
	default:
		return x * exp(x*x, (n-1)/2)
	}
}
 
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 {
    x.pow(n)
}
33
Atomically read and update variable
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. 
var lock sync.Mutex

lock.Lock()
x = f(x)
lock.Unlock()
 
let mut x = x.lock().unwrap();
*x = f(x);
34
Create a set of objects
Declare and initialize a set x containing unique objects of type T. 
x := make(map[T]bool)
Alternative implementation:
x := make(map[T]struct{})
 
let x: HashSet<T> = HashSet::new();
35
First-class function : compose
Implement a function compose (A -> C) with parameters f (A -> B) and g (B -> C), which returns the composition function g ∘ f 
func compose(f func(A) B, g func(B) C) func(A) C {
	return func(x A) C {
		return g(f(x))
	}
}
 
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))
}
36
First-class function : generic composition
Implement a function compose which returns composition function g ∘ f for any functions f and g having exactly 1 parameter. 
func composeIntFuncs(f func(int) int, g func(int) int) func(int) int {
	return func(x int) int {
		return g(f(x))
	}
}
Alternative implementation:
func compose[T, U, V any](f func(T) U, g func(U) V) func(T) V {
	return func(x T) V {
		return g(f(x))
	}
}
 
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))
}
37
Currying
Transform a function that takes multiple arguments into a function for which some of the arguments are preset. 
type PayFactory func(Company, *Employee, *Employee) Payroll

type CustomPayFactory func(*Employee) Payroll

func CurryPayFactory(pf PayFactory,company Company, boss *Employee) CustomPayFactory {
	return func(e *Employee) Payroll {
		return pf(company, boss, e)
	}
}
 
fn add(a: u32, b: u32) -> u32 {
    a + b
}

let add5 = move |x| add(5, x);
38
Extract a substring
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. 
t := string([]rune(s)[i:j])
 
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];
39
Check if string contains a word
Set the boolean ok to true if the string word is contained in string s as a substring, or to false otherwise. 
ok := strings.Contains(s, word)
 
let ok = s.contains(word);
40
Graph with adjacency lists
Declare a Graph data structure in which each Vertex has a collection of its neighbouring vertices. 
type Vertex struct{
	Id int
	Label string
	Neighbours map[*Vertex]bool
}

type Graph []*Vertex
Alternative implementation:
type Graph[L any] []*Vertex[L]

type Vertex[L any] struct {
	Label      L
	Neighbours map[*Vertex[L]]bool
}
41
Reverse a string
Create the string t containing the same characters as the string s, in reverse order.
The original string s must remain unaltered. Each character must be handled correctly regardless its number of bytes in memory. 
runes := []rune(s)
for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
   runes[i], runes[j] = runes[j], runes[i]
}
t := string(runes)
Alternative implementation:
func reverse(s string) string {
	if len(s) <= 1 {
		return s
	}
	var b strings.Builder
	b.Grow(len(s))
	for len(s) > 0 {
		r, l := utf8.DecodeLastRuneInString(s)
		s = s[:len(s)-l]
		b.WriteRune(r)
	}
	return b.String()
}
Alternative implementation:
runes := []rune(s)
slices.Reverse(runes)
t := string(runes)
 
let t = s.chars().rev().collect::<String>();
Alternative implementation:
let t: String = s.chars().rev().collect();
42
Continue outer loop
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. 
mainloop:
	for _, v := range a {
		for _, w := range b {
			if v == w {
				continue mainloop
			}
		}
		fmt.Println(v)
	}
 
'outer: for va in &a {
    for vb in &b {
        if va == vb {
            continue 'outer;
        }
    }
    println!("{}", va);
}
43
Break outer loop
Look for a negative value v in 2D integer matrix m. Print it and stop searching. 
mainloop:
	for i, line := range m {
		for _, v := range line {
			if v < 0 {
				fmt.Println(v)
				break mainloop
			}
		}
	}
 
'outer: for v in m {
    'inner: for i in v {
        if i < 0 {
            println!("Found {}", i);
            break 'outer;
        }
    }
}
44
Insert element in list
Insert the element x at position i in the list s. Further elements must be shifted to the right. 
s = append(s, 0)
copy(s[i+1:], s[i:])
s[i] = x
Alternative implementation:
s = slices.Insert(s, i, x)
 
s.insert(i, x);
45
Pause execution for 5 seconds
Sleep for 5 seconds in current thread, before proceeding with the next instructions. 
time.Sleep(5 * time.Second)
 
thread::sleep(time::Duration::from_secs(5));
46
Extract beginning of string (prefix)
Create the string t consisting of the 5 first characters of the string s.
Make sure that multibyte characters are properly handled. 
t := s
r := []rune(s)
if len(r) > 5 {
	t = string(r[:5])
}
Alternative implementation:
i := 0
count := 0
for i = range s {
	if count >= 5 {
		break
	}
	count++
}
t := s
if count >= 5 {
	t = s[:i]
}
 
let t = s.char_indices().nth(5).map_or(s, |(i, _)| &s[..i]);
Alternative implementation:
let t = s.chars().take(5).collect::<String>();
47
Extract string suffix
Create string t consisting in the 5 last characters of string s.
Make sure that multibyte characters are properly handled. 
t := string([]rune(s)[len([]rune(s))-5:])
Alternative implementation:
i := len(s)
for j := 0; i > 0 && j < 5; j++ {
	_, size := utf8.DecodeLastRuneInString(s[0:i])
	i -= size
}
t := s[i:]
 
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..]);
48
Multi-line string literal
Assign to variable s a string literal consisting in several lines of text, including newlines. 
s := `Huey
Dewey
Louie`
 
let s = "line 1
line 2
line 3";
Alternative implementation:
let s = r#"Huey
Dewey
Louie"#;
49
Split a space-separated string
Build list chunks consisting in substrings of the string s, separated by one or more space characters. 
chunks := strings.Split(s, " ")
Alternative implementation:
chunks := strings.Fields(s)
 
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();
50
Make an infinite loop
Write a loop that has no end clause. 
for {
	// Do something
}
 
loop {
	// Do something
}
51
Check if map contains key
Determine whether the map m contains an entry for the key k 
_, ok := m[k]
 
m.contains_key(&k)
52
Check if map contains value
Determine whether the map m contains an entry with the value v, for some key. 
func containsValue(m map[K]T, v T) bool {
	for _, x := range m {
		if x == v {
			return true
		}
	}
	return false
}
Alternative implementation:
func containsValue[M ~map[K]V, K, V comparable](m M, v V) bool {
	for _, x := range m {
		if x == v {
			return true
		}
	}
	return false
}
 
let does_contain = m.values().any(|&val| *val == v);
53
Join a list of strings
Concatenate elements of string list x joined by the separator ", " to create a single string y. 
y := strings.Join(x, ", ")
 
let y = x.join(", ");
54
Compute sum of integers
Calculate the sum s of the integer list or array x. 
s := 0
for _, v := range x {
	s += v
}
 
x.iter().sum()
Alternative implementation:
let s = x.iter().sum::<i32>();
55
Convert integer to string
Create the string representation s (in radix 10) of the integer value i. 
s := strconv.Itoa(i)
Alternative implementation:
s := strconv.FormatInt(i, 10)
Alternative implementation:
s := fmt.Sprintf("%d", i)
 
let s = i.to_string();
Alternative implementation:
let s = format!("{}", i);
56
Launch 1000 parallel tasks and wait for completion
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". 
var wg sync.WaitGroup
wg.Add(1000)
for i := 1; i <= 1000; i++ {
	go func(i int) {
		f(i)
		wg.Done()
	}(i)
}
wg.Wait()
fmt.Println("Finished")
 
let threads: Vec<_> = (0..1000).map(|i| thread::spawn(move || f(i))).collect();

for t in threads {
	t.join();
}
57
Filter list
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. 
y := make([]T, 0, len(x))
for _, v := range x{
	if p(v){
		y = append(y, v)
	}
}
Alternative implementation:
n := 0
for _, v := range x {
	if p(v) {
		n++
	}
}
y := make([]T, 0, n)
for _, v := range x {
	if p(v) {
		y = append(y, v)
	}
}
Alternative implementation:
func filter[S ~[]T, T any](x S, p func(T) bool) S {
	var y S
	for _, v := range x {
		if p(v) {
			y = append(y, v)
		}
	}
	return y
}
Alternative implementation:
del := func(t *T) bool { return !p(t) }

y := slices.DeleteFunc(slices.Clone(x), del)
 
let y: Vec<_> = x.iter().filter(p).collect();
58
Extract file content to a string
Create the string lines from the content of the file with filename f. 
b, err := os.ReadFile(f)
if err != nil {
	// Handle error...
}
lines := string(b)
 
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.");
59
Write to standard error stream
Print the message "x is negative" to standard error (stderr), with integer x value substitution (e.g. "-2 is negative"). 
fmt.Fprintln(os.Stderr, x, "is negative")
 
eprintln!("{} is negative", x);
60
Read command line argument
Assign to x the string value of the first command line parameter, after the program name. 
x := os.Args[1]
 
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());
61
Get current date
Assign to the variable d the current date/time value, in the most standard type. 
d := time.Now()
 
let d = time::now();
Alternative implementation:
let d = SystemTime::now();
62
Find substring position
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. 
i := strings.Index(x, y)
 
let i = x.find(y);
63
Replace fragment of a string
Assign to x2 the value of string x with all occurrences of y replaced by z.
Assume occurrences of y are not overlapping. 
x2 := strings.Replace(x, y, z, -1)
Alternative implementation:
x2 := strings.ReplaceAll(x, y, z)
 
let x2 = x.replace(&y, &z);
64
Big integer : value 3 power 247
Assign to x the value 3^247 
x := new(big.Int)
x.Exp(big.NewInt(3), big.NewInt(247), nil)
 
let a = 3.to_bigint().unwrap();
let x = num::pow(a, 247);
65
Format decimal number
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%" 
s := fmt.Sprintf("%.1f%%", 100.0*x)
 
let s = format!("{:.1}%", 100.0 * x);
66
Big integer exponentiation
Calculate the result z of x power n, where x is a big integer and n is a positive integer. 
nb := big.NewInt(int64(n))
var z big.Int
z.Exp(x, nb, nil)
 
let z = num::pow(x, n);
67
Binomial coefficient "n choose k"
Calculate binom(n, k) = n! / (k! * (n-k)!). Use an integer type able to handle huge numbers. 
z := new(big.Int)
z.Binomial(n, k)
 
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();
    }
    res
}
68
Create a bitset
Create an object x to store n bits (n being potentially large). 
var x *big.Int = new(big.Int)
Alternative implementation:
x := make([]bool, n)
Alternative implementation:
x := make([]uint64, (n+63)/64)
 
let mut x = vec![false; n];
69
Seed random generator
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. 
r := rand.New(rand.NewSource(s))
Alternative implementation:
r := rand.New(rand.NewPCG(s, s))
 
let s = 32;
let mut rng = StdRng::seed_from_u64(s);
70
Use clock as random generator seed
Get the current datetime and provide it as a seed to a random generator. The generator sequence will be different at each run. 
r := rand.New(rand.NewSource(time.Now().UnixNano()))
 
let d = SystemTime::now()
    .duration_since(SystemTime::UNIX_EPOCH)
    .expect("Duration since UNIX_EPOCH failed");
let mut rng = StdRng::seed_from_u64(d.as_secs());
71
Echo program implementation
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. 
func main() {
    fmt.Println(strings.Join(os.Args[1:], " "))
}
 
println!("{}", env::args().skip(1).collect::<Vec<_>>().join(" "));
Alternative implementation:
println!("{}", std::env::args().skip(1).format(" "));
73
Create a factory
Create a factory named fact for any sub class of Parent and taking exactly one string str as constructor parameter. 
type ParentFactory func(string) Parent

var fact ParentFactory = func(str string) Parent {
	return Parent{
		name: str,
	}
}
 
fn fact<Parent: std::str::FromStr>(str: String, _: Parent) -> Parent where <Parent as FromStr>::Err: Debug 
{
    return str.parse::<Parent>().unwrap();
}
74
Compute GCD
Compute the greatest common divisor x of big integers a and b. Use an integer type able to handle huge numbers. 
x.GCD(nil, nil, a, b)
 
let x = a.gcd(&b);
75
Compute LCM
Compute the least common multiple x of big integers a and b. Use an integer type able to handle huge numbers. 
gcd.GCD(nil, nil, a, b)
x.Div(a, gcd).Mul(x, b)
 
let x = a.lcm(&b);
76
Binary digits from an integer
Create the string s of integer x written in base 2.

E.g. 13 -> "1101" 
s := strconv.FormatInt(x, 2)
Alternative implementation:
s := fmt.Sprintf("%b", x)
 
let s = format!("{:b}", x);
Alternative implementation:
let s = format!("{x:b}");
77
Complex number
Declare a complex x and initialize it with value (3i - 2). Then multiply it by i. 
x := 3i - 2
x *= 1i
 
let mut x = Complex::new(-2, 3);
x *= Complex::i();
78
"do while" loop
Execute a block once, then execute it again as long as boolean condition c is true. 
for{
   someThing()
   someOtherThing()
   if !c {
     break
   }
}
Alternative implementation:
for done := false; !done; {
	someThing()
	someOtherThing()
	done = !c()
}
 
loop {
    doStuff();
    if !c { break; }
}
Alternative implementation:
while {
   doStuff();
   c
} { /* EMPTY */ }
79
Convert integer to floating point number
Declare the floating point number y and initialize it with the value of the integer x . 
y := float64(x)
 
let y = x as f64;
80
Truncate floating point number to integer
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). 
y := int(x)
 
let y = x as i32;
81
Round floating point number to integer
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). 
y := int(math.Floor(x + 0.5))
 
let y = x.round() as i64;
82
Count substring occurrences
Find how many times string s contains substring t.
Specify if overlapping occurrences are counted. 
x := strings.Count(s, t)
 
let c = s.matches(t).count();
83
Regex with character repetition
Declare regular expression r matching the strings "http", "htttp", "httttp", etc. 
r := regexp.MustCompile("htt+p")
 
let r = Regex::new(r"htt+p").unwrap();
84
Count bits set in integer binary representation
Count number c of 1s in the integer i in base 2.

E.g. i=6 → c=2 
func PopCountUInt64(i uint64) (c int) {
	i -= (i >> 1) & 0x5555555555555555
	i = (i>>2)&0x3333333333333333 + i&0x3333333333333333
	i += i >> 4
	i &= 0x0f0f0f0f0f0f0f0f
	i *= 0x0101010101010101
	return int(i >> 56)
}

func PopCountUInt32(i uint32) (n int) {
	i -= (i >> 1) & 0x55555555
	i = (i>>2)&0x33333333 + i&0x33333333
	i += i >> 4
	i &= 0x0f0f0f0f
	i *= 0x01010101
	return int(i >> 24)
}
Alternative implementation:
c := bits.OnesCount(i)
 
let c = i.count_ones();
85
Check if integer addition will overflow
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. 
func addingWillOverflow(x int, y int) bool {
	if x > 0 {
		return y > math.MaxInt-x
	}
	return y < math.MinInt-x
}
 
fn adding_will_overflow(x: usize, y: usize) -> bool {
    x.checked_add(y).is_none()
}
86
Check if integer multiplication will overflow
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. 
func multiplyWillOverflow(x, y uint64) bool {
   if x <= 1 || y <= 1 {
     return false
   }
   d := x * y
   return d/y != x
}
 
fn multiply_will_overflow(x: i64, y: i64) -> bool {
    x.checked_mul(y).is_none()
}
87
Stop program
Exit immediately.
If some extra cleanup work is executed by the program runtime (not by the OS itself), describe it. 
os.Exit(0)
 
std::process::exit(0);
88
Allocate 1M bytes
Create a new bytes buffer buf of size 1,000,000. 
buf := make([]byte, 1_000_000)
 
let buf: Vec<u8> = Vec::with_capacity(1000000);
89
Handle invalid argument
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. 
return nil, fmt.Errorf("invalid value for x: %v", x)
 
enum CustomError { InvalidAnswer }

fn do_stuff(x: i32) -> Result<i32, CustomError> {
    if x != 42 {
        Err(CustomError::InvalidAnswer)
    } else {
        Ok(x)
    }
}
90
Read-only outside
Expose a read-only integer x to the outside world while being writable inside a structure or a class Foo. 
type Foo struct {
	x int
}

func (f *Foo) X() int {
	return f.x
}
 
struct Foo {
    x: usize
}

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

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

    pub fn bar(&mut self) {
        self.x += 1;
    }
}
91
Load JSON file into object
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. 
buffer, err := os.ReadFile("data.json")
if err != nil {
	return err
}
err = json.Unmarshal(buffer, &x)
if err != nil {
	return err
}
Alternative implementation:
r, err := os.Open(filename)
if err != nil {
	return err
}
decoder := json.NewDecoder(r)
err = decoder.Decode(&x)
if err != nil {
	return err
}
 
let x = ::serde_json::from_reader(File::open("data.json")?)?;
92
Save object into JSON file
Write the contents of the object x into the file data.json. 
buffer, err := json.MarshalIndent(x, "", "  ")
if err != nil {
	return err
}
err = os.WriteFile("data.json", buffer, 0644)
 
::serde_json::to_writer(&File::create("data.json")?, &x)?
93
Pass a runnable procedure as parameter
Implement the procedure control which receives one parameter f, and runs f. 
func control(f func()) {
	f()
}
 
fn control(f: impl Fn()) {
    f();
}
94
Print the type of a variable
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. 
fmt.Println(reflect.TypeOf(x))
Alternative implementation:
fmt.Printf("%T", x)
 
fn type_of<T>(_: &T) -> &'static str {
    std::intrinsics::type_name::<T>()
}

println!("{}", type_of(&x));
95
Get file size
Assign to variable x the length (number of bytes) of the local file at path. 
info, err := os.Stat(path)
if err != nil {
	return err
}
x := info.Size()
 
let x = fs::metadata(path)?.len();
Alternative implementation:
let x = path.metadata()?.len();
Alternative implementation:
let x = fs::metadata(path)?.st_size();
96
Check string prefix
Set the boolean b to true if string s starts with prefix prefix, false otherwise. 
b := strings.HasPrefix(s, prefix)
 
let b = s.starts_with(prefix);
97
Check string suffix
Set boolean b to true if string s ends with string suffix, false otherwise. 
b := strings.HasSuffix(s, suffix)
 
let b = s.ends_with(suffix);
98
Epoch seconds to date object
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 
d := time.Unix(ts, 0)
 
let d = NaiveDateTime::from_timestamp(ts, 0);
99
Format date YYYY-MM-DD
Assign to the string x the value of the fields (year, month, day) of the date d, in format YYYY-MM-DD. 
x := d.Format("2006-01-02")
 
Utc::today().format("%Y-%m-%d")
Alternative implementation:
let format = format_description!("[year]-[month]-[day]");
let x = d.format(&format).expect("Failed to format the date");
100
Sort by a comparator
Sort elements of array-like collection items, using a comparator c. 
type ItemCSorter []Item
func (s ItemCSorter) Len() int           { return len(s) }
func (s ItemCSorter) Less(i, j int) bool { return c(s[i], s[j]) }
func (s ItemCSorter) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }

func sortItems(items []Item) {
	sorter := ItemCSorter(items)
	sort.Sort(sorter)
}
Alternative implementation:
type ItemsSorter struct {
	items []Item
	c     func(x, y Item) bool
}

func (s ItemsSorter) Len() int           { return len(s.items) }
func (s ItemsSorter) Less(i, j int) bool { return s.c(s.items[i], s.items[j]) }
func (s ItemsSorter) Swap(i, j int)      { s.items[i], s.items[j] = s.items[j], s.items[i] }

func sortItems(items []Item, c func(x, y Item) bool) {
	sorter := ItemsSorter{
		items,
		c,
	}
	sort.Sort(sorter)
}
Alternative implementation:
sort.Slice(items, func(i, j int) bool {
	return c(items[i], items[j])
})
Alternative implementation:
slices.SortFunc(items, c)
 
items.sort_by(c);
101
Load from HTTP GET request into a string
Make an HTTP request with method GET to the URL u, then store the body of the response in the string s. 
res, err := http.Get(u)
if err != nil {
	return err
}
buffer, err := io.ReadAll(res.Body)
res.Body.Close()
if err != nil {
	return err
}
s := string(buffer)
 
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)?;
102
Load from HTTP GET request into a file
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. 
out, err := os.Create("result.txt")
if err != nil {
	return err
}
defer out.Close()

resp, err := http.Get(u)
if err != nil {
	return err
}
defer func() {
	io.Copy(io.Discard, resp.Body)
	resp.Body.Close()
}()
if resp.StatusCode != 200 {
	return fmt.Errorf("Status: %v", resp.Status)
}

_, err = io.Copy(out, resp.Body)
if err != nil {
	return err
}
 
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),
};
103
Load XML file into struct
Read from the file data.xml and write its contents into the object x.
Assume the XML data is suitable for the type of x. 
buffer, err := os.ReadFile("data.xml")
if err != nil {
	return err
}
err = xml.Unmarshal(buffer, &x)
if err != nil {
	return err
}
104
Save object into XML file
Write the contents of the object x into the file data.xml. 
buffer, err := xml.MarshalIndent(x, "", "  ")
if err != nil {
	return err
}
err = os.WriteFile("data.xml", buffer, 0644)
105
Current executable name
Assign to the string s the name of the currently executing program (but not its full path). 
path := os.Args[0]
s = filepath.Base(path)
Alternative implementation:
path, err := os.Executable()
if err != nil {
  panic(err)
}
s = filepath.Base(path)
 
fn get_exec_name() -> Option<String> {
    std::env::current_exe()
        .ok()
        .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")
    .file_name()
    .expect("Can't get the exec name")
    .to_string_lossy()
    .into_owned();
106
Get program working directory
Assign to string dir the path of the working directory.
(This is not necessarily the folder containing the executable itself) 
dir, err := os.Getwd()
 
let dir = env::current_dir().unwrap();
107
Get folder containing current program
Assign to string dir the path of the folder containing the currently running executable.
(This is not necessarily the working directory, though.) 
programPath := os.Args[0]
absolutePath, err := filepath.Abs(programPath)
if err != nil {
	return err
}
dir := filepath.Dir(absolutePath)
 
let dir = std::env::current_exe()?
    .canonicalize()
    .expect("the current exe should exist")
    .parent()
    .expect("the current exe should be a file")
    .to_string_lossy()
    .to_owned();
109
Number of bytes of a type
Set n to the number of bytes of a variable t (of type T). 
var t T
tType := reflect.TypeOf(t)
n := tType.Size()
 
let n = std::mem::size_of::<T>();
110
Check if string is blank
Set the boolean blank to true if the string s is empty, or null, or contains only whitespace ; false otherwise. 
blank := strings.TrimSpace(s) == ""
 
let blank = s.trim().is_empty();
Alternative implementation:
let blank = s.chars().all(|c| c.is_whitespace());
111
Launch other program
From current process, run program x with command-line parameters "a", "b". 
err := exec.Command("x", "a", "b").Run()
 
let output = Command::new("x")
    .args(&["a", "b"])
    .spawn()
    .expect("failed to execute process");
Alternative implementation:
let output = Command::new("x")
        .args(&["a", "b"])
        .output()
        .expect("failed to execute process");
Alternative implementation:
let output = Command::new("x")
        .args(&["a", "b"])
        .status()
        .expect("failed to execute process");
112
Iterate over map entries, ordered by keys
Print each key k with its value x from an associative array mymap, in ascending order of k. 
keys := make([]string, 0, len(mymap))
for k := range mymap {
	keys = append(keys, k)
}
sort.Strings(keys)

for _, k := range keys {
	x := mymap[k]
	fmt.Println("Key =", k, ", Value =", x)
}
Alternative implementation:
keys := maps.Keys(mymap)
slices.Sort(keys)

for _, k := range keys {
	x := mymap[k]
	fmt.Println("Key =", k, ", Value =", x)
}
Alternative implementation:
keys := maps.Keys(mymap)
slices.SortFunc(keys, compare)

for _, k := range keys {
	x := mymap[k]
	fmt.Println("Key =", k, ", Value =", x)
}
 
for (k, x) in mymap {
    println!("({}, {})", k, x);
}
113
Iterate over map entries, ordered by values
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. 
type entry struct {
	key   string
	value int
}

type entries []entry
func (list entries) Len() int { return len(list) }
func (list entries) Less(i, j int) bool { return list[i].value < list[j].value }
func (list entries) Swap(i, j int) { list[i], list[j] = list[j], list[i] }

entries := make(entries, 0, len(mymap))
for k, x := range mymap {
	entries = append(entries, entry{key: k, values: x})
}
sort.Sort(entries)

for _, e := range entries {
	fmt.Println("Key =", e.key, ", Value =", e.value)
}
Alternative implementation:
type entry struct {
	key   string
	value int
}

entries := make([]entry, 0, len(mymap))
for k, x := range mymap {
	entries = append(entries, entry{key: k, value: x})
}
sort.Slice(entries, func(i, j int) bool {
	return entries[i].value < entries[j].value
})

for _, e := range entries {
	fmt.Println("Key =", e.key, ", Value =", e.value)
}
 
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);
}
114
Test deep equality
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. 
b := reflect.DeepEqual(x, y)
 
let b = x == y;
115
Compare dates
Set boolean b to true if date d1 is strictly before date d2 ; false otherwise. 
b := d1.Before(d2)
 
let b = d1 < d2;
116
Remove occurrences of word from string
Remove all occurrences of string w from string s1, and store the result in s2. 
s2 := strings.Replace(s1, w, "", -1)
Alternative implementation:
s2 := strings.ReplaceAll(s1, w, "")
 
s2 = s1.replace(w, "");
Alternative implementation:
let s2 = str::replace(s1, w, "");
117
Get list size
Set n to the number of elements of the list x. 
n := len(x)
 
let n = x.len();
118
List to set
Create the set y from the list x.
x may contain duplicates. y is unordered and has no repeated values. 
y := make(map[T]struct{}, len(x))
for _, v := range x {
	y[v] = struct{}{}
}
Alternative implementation:
func sliceToSet[T comparable](x []T) map[T]struct{} {
	y := make(map[T]struct{}, len(x))
	for _, v := range x {
		y[v] = struct{}{}
	}
	return y
}
 
let y: HashSet<_> = x.into_iter().collect();
119
Deduplicate list
Remove duplicates from the list x.
Explain if the original order is preserved. 
y := make(map[T]struct{}, len(x))
for _, v := range x {
	y[v] = struct{}{}
}
x2 := make([]T, 0, len(y))
for _, v := range x {
	if _, ok := y[v]; ok {
		x2 = append(x2, v)
		delete(y, v)
	}
}
x = x2
Alternative implementation:
seen := make(map[T]bool)
j := 0
for _, v := range x {
	if !seen[v] {
		x[j] = v
		j++
		seen[v] = true
	}
}
x = x[:j]
Alternative implementation:
seen := make(map[T]bool)
j := 0
for _, v := range x {
	if !seen[v] {
		x[j] = v
		j++
		seen[v] = true
	}
}
for i := j; i < len(x); i++ {
	x[i] = nil
}
x = x[:j]
Alternative implementation:
func deduplicate[S ~[]T, T comparable](x S) S {
	seen := make(map[T]bool)
	j := 0
	for _, v := range x {
		if !seen[v] {
			x[j] = v
			j++
			seen[v] = true
		}
	}
	var zero T
	for i := j; i < len(x); i++ {
		// Avoid memory leak
		x[i] = zero
	}
	return x[:j]
}
Alternative implementation:
slices.Sort(x)
x = slices.Compact(x)

x.sort();
x.dedup();
Alternative implementation:
let dedup: Vec<_> = x.iter().unique().collect();
120
Read integer from stdin
Read an integer value from the standard input into the variable n 
_, err := fmt.Scan(&n)
Alternative implementation:
_, err := fmt.Scanf("%d", &n)
 
fn get_input() -> String {
    let mut buffer = String::new();
    std::io::stdin().read_line(&mut buffer).expect("Failed");
    buffer
}

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()
    .lock()
    .lines()
    .next()
    .expect("stdin should be available")
    .expect("couldn't read from stdin")
    .trim()
    .parse()
    .expect("input was not an integer");
Alternative implementation:
let n: i32 = read!();
121
UDP listen and read
Listen UDP traffic on port p and read 1024 bytes into the buffer b. 
ServerAddr,err := net.ResolveUDPAddr("udp",p)
if err != nil {
	return err
}
ServerConn, err := net.ListenUDP("udp", ServerAddr)
if err != nil {
	return err
}
defer ServerConn.Close()
n,addr,err := ServerConn.ReadFromUDP(b[:1024])
if err != nil {
	return err
}
if n<1024 {
	return fmt.Errorf("Only %d bytes could be read.", n)
}
 
let mut b = [0 as u8; 1024];
let sock = UdpSocket::bind(("localhost", p)).unwrap();
sock.recv_from(&mut b).unwrap();
122
Declare an enumeration
Create an enumerated type Suit with 4 possible values SPADES, HEARTS, DIAMONDS, CLUBS. 
type Suit int

const (
  Spades Suit = iota
  Hearts
  Diamonds
  Clubs
)
 
enum Suit {
    Spades,
    Hearts,
    Diamonds,
    Clubs,
}
123
Assert condition
Verify that predicate isConsistent returns true, otherwise report assertion violation.
Explain if the assertion is executed even in production environment or not. 
if !isConsistent() {
	panic("State consistency violated")
}
 
assert!(is_consistent);
124
Binary search for a value in sorted array
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. 
func binarySearch(a []T, x T) int {
	imin, imax := 0, len(a)-1
	for imin <= imax {
		imid := imin + (imax-imin) / 2
		switch {
		case a[imid] == x:
			return imid
		case a[imid] < x:
			imin = imid + 1
		default:
			imax = imid - 1
		}
	}
	return -1
}
Alternative implementation:
func binarySearch(a []int, x int) int {
	i := sort.SearchInts(a, x)
	if i < len(a) && a[i] == x {
		return i
	}
	return -1
}
Alternative implementation:
func binarySearch(a []T, x T) int {
	f := func(i int) bool { return a[i] >= x }
	i := sort.Search(len(a), f)
	if i < len(a) && a[i] == x {
		return i
	}
	return -1
}
Alternative implementation:
func binarySearch(a []T, x T) int {
	if i, ok := slices.BinarySearch(a, x); ok {
		return i
	} else {
		return -1
	}
}
 
a.binary_search(&x).unwrap_or(-1);
125
Measure function call duration
measure the duration t, in nanoseconds, of a call to the function foo. Print this duration. 
t1 := time.Now()
foo()
t := time.Since(t1)
ns := int64(t / time.Nanosecond)
fmt.Printf("%dns\n", ns)
Alternative implementation:
t1 := time.Now()
foo()
t := time.Since(t1)
ns := t.Nanoseconds()
fmt.Printf("%dns\n", ns)
 
let start = Instant::now();
foo();
let duration = start.elapsed();
println!("{}", duration);
126
Multiple return values
Write a function foo that returns a string and a boolean value. 
func foo() (string, bool) {
	return "Too good to be", true
}
 
fn foo() -> (String, bool) {
    (String::from("bar"), true)
}
127
Source code inclusion
Import the source code for the function foo body from a file "foobody.txt". 
//go:embed foobody.txt
var s string


fn main() {
    include!("foobody.txt");
}
128
Breadth-first traversing of a tree
Call a function f on every node of a tree, in breadth-first prefix order 
func (root *Tree) Bfs(f func(*Tree)) {
	if root == nil {
		return
	}
	queue := []*Tree{root}
	for len(queue) > 0 {
		t := queue[0]
		queue = queue[1:]
		f(t)
		queue = append(queue, t.Children...)
	}
}
 
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();
        q.push_back(self);

        while let Some(t) = q.pop_front() {
            (f)(&t.value);
            for child in &t.children {
                q.push_back(child);
            }
        }
    }
}
129
Breadth-first traversal in a graph
Call the function f on every vertex accessible from the vertex start, in breadth-first prefix order 
func (start *Vertex) Bfs(f func(*Vertex)) {
	queue := []*Vertex{start}
	seen := map[*Vertex]bool{start: true}
	for len(queue) > 0 {
		v := queue[0]
		queue = queue[1:]
		f(v)
		for next, isEdge := range v.Neighbours {
			if isEdge && !seen[next] {
				queue = append(queue, next)
				seen[next] = true
			}
		}
	}
}
 
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;
	    (f)(&v.borrow().value);
	    for n in &v.borrow().neighbours {
	        let n = n.upgrade().expect("Invalid neighbour");
	        if q.iter().all(|v| v.as_ptr() != n.as_ptr()) {
	            q.push(n);
	        }
	    }
	}
}
130
Depth-first traversal in a graph
Call th function f on every vertex accessible from the vertex v, in depth-first prefix order 
func (v *Vertex) Dfs(f func(*Vertex), seen map[*Vertex]bool) {
	seen[v] = true
	f(v)
	for next, isEdge := range v.Neighbours {
		if isEdge && !seen[next] {
			next.Dfs(f, seen)
		}
	}
}
Alternative implementation:
func (v *Vertex[L]) Dfs(f func(*Vertex[L]), seen map[*Vertex[L]]bool) {
	seen[v] = true
	f(v)
	for next, isEdge := range v.Neighbours {
		if isEdge && !seen[next] {
			next.Dfs(f, seen)
		}
	}
}
 
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>>) {
	s.push(start.as_ptr());
	(f)(&start.borrow().value);
	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);
		}
	}
}
131
Successive conditions
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. 
switch {
case c1:
	f1()
case c2:
	f2()
case c3:
	f3()
}
 
if c1 { f1() } else if c2 { f2() } else if c3 { f3() }
Alternative implementation:
match true {
    _ if c1 => f1(),
    _ if c2 => f2(),
    _ if c3 => f3(),
    _ => (),
}
132
Measure duration of procedure execution
Run the procedure f, and return the duration of the execution of f. 
func clock(f func()) time.Duration {
	t := time.Now()
	f()
	return time.Since(t)
}
 
let start = Instant::now();
f();
let duration = start.elapsed();
133
Case-insensitive string contains
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. 
lowerS, lowerWord := strings.ToLower(s), strings.ToLower(word)
ok := strings.Contains(lowerS, lowerWord)
 
let re = Regex::new(&format!("(?i){}", regex::escape(word))).unwrap();
let ok = re.is_match(&s);
Alternative implementation:
let re =
    RegexBuilder::new(&regex::escape(word))
    .case_insensitive(true)
    .build().unwrap();

let ok = re.is_match(s);
Alternative implementation:
let ok = s.to_ascii_lowercase().contains(&word.to_ascii_lowercase());
134
Create a new list
Declare and initialize a new list items, containing 3 elements a, b, c. 
items := []T{a, b, c}
 
let items = vec![a, b, c];
135
Remove item from list, by its value
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. 
for i, y := range items {
	if y == x {
		items = append(items[:i], items[i+1:]...)
		break
	}
}
Alternative implementation:
for i, y := range items {
	if y == x {
		copy(items[i:], items[i+1:])
		items[len(items)-1] = nil
		items = items[:len(items)-1]
		break
	}
}
Alternative implementation:
func removeFirstByValue[S ~[]T, T comparable](items *S, x T) {
	for i, y := range *items {
		if y == x {
			*items = slices.Delete(*items, i, i+1)
			return
		}
	}
}
Alternative implementation:
func removeFirstByValue[S ~[]T, T comparable](items *S, x T) {
	if i := slices.Index(*items, x); i != -1 {
		*items = slices.Delete(*items, i, i+1)
	}
}
 
if let Some(i) = items.iter().position(|item| *item == x) {
    items.remove(i);
}
136
Remove all occurrences of a value from a list
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. 
items2 := make([]T, 0, len(items))
for _, v := range items {
	if v != x {
		items2 = append(items2, v)
	}
}
Alternative implementation:
j := 0
for i, v := range items {
	if v != x {
		items[j] = items[i]
		j++
	}
}
items = items[:j]
Alternative implementation:
j := 0
for i, v := range items {
	if v != x {
		items[j] = items[i]
		j++
	}
}
for k := j; k < len(items); k++ {
	items[k] = nil
}
items = items[:j]
Alternative implementation:
func removeAll[S ~[]T, T comparable](items *S, x T) {
	j := 0
	for i, v := range *items {
		if v != x {
			(*items)[j] = (*items)[i]
			j++
		}
	}
	var zero T
	for k := j; k < len(*items); k++ {
		(*items)[k] = zero
	}
	*items = (*items)[:j]
}
Alternative implementation:
items = slices.DeleteFunc(items, func(e T) bool {
	return e == x
})
 
items = items.into_iter().filter(|&item| item != x).collect();
Alternative implementation:
items.retain(|&item| item != x);
137
Check if string contains only digits
Set the boolean b to true if the string s contains only characters in the range '0'..'9', false otherwise. 
b := true
for _, c := range s {
	if c < '0' || c > '9' {
		b = false
		break
	}
}
Alternative implementation:
isNotDigit := func(c rune) bool { return c < '0' || c > '9' }
b := strings.ContainsFunc(s, isNotDigit) 
let chars_are_numeric: Vec<bool> = s.chars()
				.map(|c|c.is_numeric())
				.collect();
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());
138
Create temp file
Create a new temporary file on the filesystem. 
tmpfile, err := os.CreateTemp("", "")
 
let temp_dir = TempDir::new("prefix")?;
let temp_file = File::open(temp_dir.path().join("file_name"))?;
139
Create temp directory
Create a new temporary folder on filesystem, for writing. 
dir, err := os.MkdirTemp("", "")
 
let tmp = TempDir::new("prefix")?;
140
Delete map entry
Delete from map m the entry having key k.

Explain what happens if k is not an existing key in m. 
delete(m, k)
 
m.remove(&k);
141
Iterate in sequence over two lists
Iterate in sequence over the elements of the list items1 then items2. For each iteration print the element. 
for _, v := range items1 {
	fmt.Println(v)
}
for _, v := range items2 {
	fmt.Println(v)
}
 
for i in item1.iter().chain(item2.iter()) {
    print!("{} ", i);
}
142
Hexadecimal digits of an integer
Assign to string s the hexadecimal representation (base 16) of integer x.

E.g. 999 -> "3e7" 
s := strconv.FormatInt(x, 16)