 # Programming-Idioms.org

3 languages side-by-side are you out of your mind that will never fit on a page
• The snippets are under the CC-BY-SA license.
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Python Rust D
1
Print a literal string on standard output
`print("Hello World")`
`println!("Hello World");`
`writeln("Hello world!");`
Alternative implementation:
`pragma(msg, "Hello World");`
2
Loop to execute some code a constant number of times
```for _ in range(10):
print("Hello")```
Alternative implementation:
`print("Hello\n"*10)`
`for _ in 0..10 { println!("Hello"); }`
Alternative implementation:
`print!("{}", "Hello\n".repeat(10));`
```foreach(i; 0..10)
writeln("Hello");```
Alternative implementation:
`iota(0,10).each!(a => "Hello".writeln);`
3
Like a function which doesn't return any value, thus has only side effects (e.g. Print to standard output)
```def finish(name):
print(f'My job here is done. Goodbye {name}')```
```fn finish(name : &str) {
println!("My job here is done. Goodbye {}", name);
}```
```void finish() {
writeln("I' m a done job");
}```
4
```def square(x):
return x*x```
Alternative implementation:
```def square(x):
return x**2```
`fn square(x : u32) -> u32 { x * x }`
```int square(int x) {
return x*x;
}```
Alternative implementation:
`alias fun = (int a){return a * a;};`
5
Declare a container type for two floating-point numbers x and y
```@dataclass
class Point:
x: float
y: float```
```struct Point {
x: f64,
y: f64,
}```
Alternative implementation:
`struct Point(f64, f64);`
```struct Point{
double x;
double y;
}

```
Alternative implementation:
```class Point
{
float x;
float y;
}```
6
Do something with each item x of an array-like collection items, regardless indexes.
```for x in items:
doSomething( x )```
```for x in items {
do_something(x);
}```
```foreach(x; items) {
doSomethingWith(x);
}```
Alternative implementation:
`items.each!(a => writeln(a))();`
7
Print each index i with its value x from an array-like collection items
```for i, x in enumerate(items):
print i, x```
```for (i, x) in items.iter().enumerate() {
println!("Item {} = {}", i, x);
}```
```foreach(i, x; items)
{
writefln("%s: %s", i, x);
}```
Alternative implementation:
`items.enumerate.each!(a => writeln("i = ", a, " value = ", a));`
8
Create a new map object x, and provide some (key, value) pairs as initial content.
`x = {"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),
].iter().cloned().collect();```
`int[string] x = ["one": 1, "two": 2];`
9
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.
```class Node:
def __init__(self, data):
self.data = data
self.left = None
self.right = None```
Alternative implementation:
```class Node:
def __init__(self, data, left_child, right_child):
self.data = data
self._left_child = left_child
self._right_child = right_child```
```struct BinTree<T> {
value: T,
left: Option<Box<BinTree<T>>>,
right: Option<Box<BinTree<T>>>,
}```
```struct BinaryTree(T)
{
T data;
BinaryTree* left;
BinaryTree* right;
}```
10
Generate a random permutation of the elements of list x
`shuffle(x)`
Alternative implementation:
`random.shuffle(list)`
```let mut rng = StdRng::new().unwrap();
rng.shuffle(&mut x);```
Alternative implementation:
```let mut rng = thread_rng();
x.shuffle(&mut rng);```
`randomShuffle(x);`
11
List x must be non-empty.
`random.choice(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();```
`x.randomSample(1);`
12
Check if list contains a value x.
list is an iterable finite container.
`x in list`
`list.contains(&x);`
Alternative implementation:
`list.iter().any(|v| v == &x)`
Alternative implementation:
`(&list).into_iter().any(|v| v == &x)`
`bool here = canFind(items, x);`
13
Access each key k with its value x from an associative array mymap, and print them.
```for k, v in mymap.items():
print(k, v)```
```for (k, x) in &mymap {
println!("Key={key}, Value={val}", key=k, val=x);
}```
```int[string] mymap = ["Hello":1 , "World":2];
foreach (k, v; mymap)
writeln("Key: ", k, " Value: ", v);```
14
Pick a random number greater than or equals to a, strictly inferior to b. Precondition : a < b.
```def pick(a,b):
return random.randrange(a, b)```
Alternative implementation:
`random.uniform(a,b)`
`thread_rng().gen_range(a..b);`
```real pick(real _a, real _b){
return uniform(_a, _b);
}```
15
Pick a random integer greater than or equals to a, inferior or equals to b. Precondition : a < b.
`random.randint(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())`
```auto x1 = uniform(a, b+1);
auto x2 = uniform!"[]"(a, b);```
16
Call a function f on every node of binary tree bt, in depth-first infix order
```def dfs(bt):
if bt is None:
return
dfs(bt.left)
f(bt)
dfs(bt.right)```
```void btTraversal(T)(BinaryTree!T bt, void function(T) f) {
if (bt.left)
btTraversal(*(bt.left), f);

f(bt.data);

if (bt.right)
btTraversal(*(bt.right), f);
}```
17
The structure must be recursive. A node may have zero or more children. A node has access to children nodes, but not to its parent.
```class Node:
def __init__(self, value, *children):
self.value = value
self.children = list(children)```
```struct Node<T> {
value: T,
children: Vec<Node<T>>,
}```
```struct Node(T){
Node[] children;
T data;
}

alias TreeOfIntegers = Node!(int);```
18
Call a function f on every node of a tree, in depth-first prefix order
```def DFS(f, root):
f(root)
for child in root:
DFS(f, child)```
```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)
}
}
// ...
}```
```void prefixOrderTraversal(alias f)(ref Tree tree)
{
f(tree);
foreach (child; tree.children)
prefixOrderTraversal!f(child);
}```
19
Reverse the order of the elements of list x.
This may reverse "in-place" and destroy the original ordering.
`x = reversed(x)`
Alternative implementation:
`y = x[::-1]`
Alternative implementation:
`x.reverse()`
`let y: Vec<_> = x.into_iter().rev().collect();`
Alternative implementation:
`x.reverse();`
`reverse(x);`
Alternative implementation:
`auto y = x.retro;`
20
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.
```def search(m, x):
for idx, item in enumerate(m):
if x in item:
return idx, item.index(x)```
```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
}```
```auto search(int[][] m, int x)
{
foreach (i, row; m)
{
foreach (j, cell; row)
{
if (cell == x)
return tuple(i, j);
}
}
}```
21
Swap values of variables a and b
`a, b = b, a`
```std::mem::swap(&mut a, &mut b);
```
Alternative implementation:
`let (a, b) = (b, a);`
```auto temp = a;
a = b;
b = temp;```
Alternative implementation:
`swap(a,b);`
22
Extract integer value i from its string representation s (in radix 10)
`i = int(s)`
`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,
};```
`auto i = s.to!int;`
23
Given real number x, create its string representation s with 2 decimal digits following the dot.
`s =  '{:.2f}'.format(x)`
Alternative implementation:
`s = f'{x:.2f}'`
`let s = format!("{:.2}", x);`
`string str = format("%.2s", x);`
24
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";`
`string s = "ネコ";`
25
Share the string value "Alan" with an existing running process which will then display "Hello, Alan"
```q = Queue()

t = Thread(target=worker)
t.daemon = True
t.start()

q.put("Alan")```
```let (send, recv) = channel();

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

send.send("Alan").unwrap();```
```auto t = spawn( {
receive( (string s) { writefln("Hello, %s", s); } );
} );

t.send("Alan");```
26
Declare and initialize a matrix x having m rows and n columns, containing real numbers.
`x = [[0 for j in xrange(n)] for i in xrange(m)]`
Alternative implementation:
`[ * n for _ in range(m)]`
`let mut x = vec![vec![0.0f64; N]; M];`
Alternative implementation:
`let mut x = [[0.0; N] ; M];`
`auto x = new double[][](m, n);`
27
Declare and initialize a 3D array x, having dimensions boundaries m, n, p, and containing real numbers.
`x = [[[0 for k in range(p)] for j in range(n)] for i in range(m)]`
Alternative implementation:
`x = numpy.zeros((m,n,p))`
`let x = vec![vec![vec![0.0f64; p]; n]; m];`
Alternative implementation:
`let x = [[[0.0f64; P]; N]; M];`
`auto x = new real[][][](m, n, p);`
28
Sort elements of 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 = sorted(items, key=lambda x: x.p)`
Alternative implementation:
`items = sorted(items, key=attrgetter('p'))`
`items.sort_by(|a,b|a.p.cmp(&b.p));`
Alternative implementation:
`items.sort_by_key(|x| x.p);`
`sort!("a.p < b.p")(items);`
29
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.
`del items[i]`
`items.remove(i)`
`items = items.remove(i);`
30
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.
```pool = Pool()
for i in range(1, 1001):
pool.apply_async(f, [i])```
```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);`
`taskPool.amap!f(iota(1, 1001));`
31
Create recursive function f which returns the factorial of non-negative integer i, calculated from f(i-1)
```def f(i):
if i == 0:
return 1
else:
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,
}
}```
```uint factorial(in uint n) pure nothrow @nogc
in {
assert(n <= 12);
} body {
if (n == 0)
return 1;
else
return n * factorial(n - 1);
}```
32
Create function exp which calculates (fast) the value x power n.
x and n are non-negative integers.
```def exp(x, n):
return x**n
```
```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),
}
}```
```uint exp(uint x, uint n) {
if(n == 0)
return 1;
if(n == 1)
return x;
if(n % 2 == 0)
return exp(x * x, n / 2);
else
return x * exp(x * x, (n - 1) / 2);
}```
33
Assign variable x the new value f(x), making sure that no other thread may modify x between the read and the write.
```lock = threading.Lock()

lock.acquire()
try:
x = f(x)
finally:
lock.release()```
Alternative implementation:
```with threading.Lock():
x = f(x)
```
```let mut x = x.lock().unwrap();
*x = f(x);```
`synchronized x = f(x);`
34
Declare and initialize a set x containing objects of type T.
```class T(object):
pass

x = set(T())```
`let x: HashSet<T> = HashSet::new();`
`auto x = redBlackTree!T;`
35
Implement a function compose (A -> C) with parameters f (A -> B) and g (B -> C), which returns composition function g ∘ f
```def compose(f, g):
return lambda a: g(f(a))```
```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))
}```
```auto compose(f, g) {
return std.functional.compose!(f, g);
}```
36
Implement a function compose which returns composition function g ∘ f for any functions f and g having exactly 1 parameter.
```def compose(f, g):
return lambda x: 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))
}```
```auto _compose(T)(T function(T) f, T function(T) g)
{
auto lambda = (T x) { return g(f(x));  };
return lambda;
}```
37
Transform a function that takes multiple arguments into a function for which some of the arguments are preset.
```def f(a):
return lambda b: a+b

print (f(2)(1))

#add_to_two = partial(f, 2)```
```fn add(a: u32, b: u32) -> u32 {
a + b
}

let add5 = move |x| add(5, x);
```
```int add(int n1, int n2)
{
return n1 + n2;
}

alias add5 = curry!(add, 5);```
38
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 = s[i:j]`
`let t = s.graphemes(true).skip(i).take(j - i).collect::<String>();`
Alternative implementation:
`let t = s.substring(i, j);`
`auto t = s[i .. j];`
39
Set boolean ok to true if string word is contained in string s as a substring, or to false otherwise.
`ok = word in s`
`let ok = s.contains(word);`
`bool ok = s.canFind(word);`
40
Declare a Graph data structure in which each Vertex has a collection of its neighbouring vertices.
```class Vertex(set): pass
class Graph(defaultdict):
def __init__(self, *paths):
self.default_factory = Vertex
for path in paths:
self.make_path(path)

def make_path(self, labels):
for l1, l2 in zip(labels, labels[1:]):
self[l1].add(l2)
self[l2].add(l1)

G = Graph((0, 1, 2, 3), (1, 4, 2))```
```struct Vertex
{
float x, y, z;
Vertex* [] adjacentVertices;
}```
41
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.
`t = s.decode('utf8')[::-1].encode('utf8')`
Alternative implementation:
`t = s[::-1]`
`let t = s.chars().rev().collect::<String>();`
Alternative implementation:
`let t: String = s.chars().rev().collect();`
`auto t = s.retro.array;`
42
Print each item v of list a which in not contained in list b.
For this, write an outer loop to iterate on a and an inner loop to iterate on b.
```for v in a:
try:
for u in b:
if v == u:
raise Exception()
print(v)
except Exception:
continue
```
```'outer: for va in &a {
for vb in &b {
if va == vb {
continue 'outer;
}
}
println!("{}", va);
}
```
```auto a = [1,2,3,4,5];
auto b = [3,5];

void main()
{
mainloop:
foreach(v;  a){
foreach(w; b){
if(v == w) continue mainloop;
}
writeln(v);
}
}
```
43
Look for a negative value v in 2D integer matrix m. Print it and stop searching.
```class BreakOuterLoop (Exception): pass

try:
position = None
for row in m:
for column in m[row]:
if m[row][column] == v:
position = (row, column)
raise BreakOuterLoop
except BreakOuterLoop:
pass```
Alternative implementation:
```def loop_breaking(m, v):
for i, row in enumerate(m):
for j, value in enumerate(row):
if value == v:
return (i, j)
return None

print(loop_breaking(([1,2,3],[4,5,6],[7,8,9]), 6))```
Alternative implementation:
```matrix = [[1,2,3],[4,-5,6],[7,8,9]]
try:
print(next(i for i in chain.from_iterable(matrix) if i < 0))
except StopIteration:
pass```
```'outer: for v in m {
'inner: for i in v {
if i < 0 {
println!("Found {}", i);
break 'outer;
}
}
}```
```outer:
foreach (i; 0 .. m.length)
{
foreach (j; 0 .. m[i].length)
{
if (m[i][j] < 0)
{
writeln(m[i][j]);
break outer;
}
}
}```
44
Insert element x at position i in list s. Further elements must be shifted to the right.
`s.insert(i, x)`
`s.insert(i, x);`
`s.insertInPlace(i, x);`
45
Sleep for 5 seconds in current thread, before proceeding with next instructions.
`time.sleep(5)`
`thread::sleep(time::Duration::from_secs(5));`
`Thread.sleep(5.seconds);`
46
Create string t consisting of the 5 first characters of string s.
Make sure that multibyte characters are properly handled.
`t = s[:5]`
```let t = s.char_indices().nth(5).map_or(s, |(i, _)| &s[..i]);
```
`string t = s[0..5];`
47
Create string t consisting in the 5 last characters of string s.
Make sure that multibyte characters are properly handled.
`t = s[-5:]`
```let last5ch = s.chars().count() - 5;
let t: String = s.chars().skip(last5ch).collect();
```
`string t = s[\$-5..\$];`
48
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"#;```
```auto s = "One,
Two,
Three
";```
Alternative implementation:
```auto s = `line1
line2
line3`;```
Alternative implementation:
```auto s = r"line1
line2
line3";```
49
Build list chunks consisting in substrings of input string s, separated by one or more space characters.
`chunks = s.split()`
`let chunks:Vec<_> = s.split_whitespace().collect();`
`auto chunks = s.splitter;`
50
Write a loop which has no end clause.
```while True:
pass```
Alternative implementation:
```while True:
a=1
```
```loop {
// Do something
}```
`while (true) { }`
Alternative implementation:
`for (;;) {}`
51
Determine whether map m contains an entry for key k
`k in m`
`m.contains_key(&k)`
`if (k in m) { }`
52
Determine whether map m contains an entry with value v, for some key.
`v in m.values()`
`let does_contain = m.values().any(|&val| *val == v);`
`m.byValue.canFind(v);`
53
Concatenate elements of string list x joined by the separator ", " to create a single string y.
```y = ', '.join(x)
```
Alternative implementation:
`y = ', '.join(map(str, x))`
`let y = x.join(", ");`
`string y = x.join(", ");`
54
Calculate the sum s of integer list x.
`s = sum(x)`
`x.iter().sum()`
Alternative implementation:
`let s = x.iter().sum::<i32>();`
`auto s = x.sum();`
55
Create the string representation s (in radix 10) of integer value i.
`s = str(i)`
`let s = i.to_string();`
Alternative implementation:
`let s = format!("{}", i);`
`string s = i.to!string;`
56
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".
```def f(i):
i * i

with Pool(1000) as p:
p.map(func=f, iterable=range(1, 1001))

print('Finished')```
```let threads: Vec<_> = (0..1000).map(|i| thread::spawn(move || f(i))).collect();

for t in threads {
t.join();
}
```
```foreach(i; parallel(iota(1,1001))){
f(i);
}
writeln("Finished");```
57
Create list y containing items from list x satisfying predicate p. Respect original ordering. Don't modify x in-place.
`y = list(filter(p, x))`
Alternative implementation:
`y = [element for element in x if p(element)]`
`let y: Vec<_> = x.iter().filter(p).collect();`
```auto y = [1, 2, 3, 4, 5].filter!(a => a%2==0);
```
Alternative implementation:
`auto y = x.filter!(p);`
58
Create string lines from the content of the file with filename f.
`lines = open(f).read()`
Alternative implementation:
```with open(f) as fo:
lines = fo.read()```
```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.");`
`string lines = cast(string) read(f, size_t.max);`
Alternative implementation:
`auto lines = f.readText;`
59
Print the message "x is negative" to standard error (stderr), with integer x value substitution (e.g. "-2 is negative").
`print(x, "is negative", file=sys.stderr)`
Alternative implementation:
`print >>sys.stderr, "%s is negative" % x`
`eprintln!("{} is negative", x);`
`stderr.writeln(x, " is negative");`
60
Assign to x the string value of the first command line parameter, after the program name.
`x = sys.argv`
```let first_arg = env::args().skip(1).next();

let fallback = "".to_owned();
let x = first_arg.unwrap_or(fallback);```
`auto x = args;`
61
Assign to variable d the current date/time value, in the most standard type.
`d = datetime.datetime.now()`
`let d = time::now();`
Alternative implementation:
`let d = SystemTime::now();`
`auto d = Clock.currTime;`
62
Set i to the position of string y inside string x, if exists.
`i = x.find(y)`
`let i = x.find(y);`
`auto i = x.countUntil(y);`
63
Assign to x2 the value of string x with all occurrences of y replaced by z.
Assume occurrences of y are not overlapping.
`x2 = x.replace(y, z)`
`let x2 = x.replace(&y, &z);`
```auto x2 = x.replace(y,z);
```
64
Assign to x the value 3^247
`x = 3**247`
```let a = 3.to_bigint().unwrap();
let x = num::pow(a, 247);```
```BigInt x = BigInt(3);
x ^^= 247;```
65
From 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 = '{:.1%}'.format(x)`
`let s = format!("{:.1}%", 100.0 * x);`
`string percent = format("%.1f%%", x * 100.0);`
66
Calculate the result z of x power n, where x is a big integer and n is a positive integer.
`z = x**n`
`let z = num::pow(x, n);`
`BigInt z = x ^^ n;`
67
Calculate binom(n, k) = n! / (k! * (n-k)!). Use an integer type able to handle huge numbers.
```def binom(n, k):
return math.factorial(n) // math.factorial(k) // math.factorial(n - k)```
Alternative implementation:
```def binom(n, k):
return math.comb(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
}```
```BigInt binom(uint n, uint k)
{
assert(n >= k);
BigInt r = 1;
for(uint i = 0; i <= k; ++i)
{
r *= n-i;
r /= i+1;
}
return r;
}```
68
Create an object x to store n bits (n being potentially large).
`x = bytearray(int(math.ceil(n / 8.0)))`
`let mut x = vec![false; n];`
```BitArray x;
x.length = n;```
69
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.
`rand = random.Random(s)`
```let s = 32;
let mut rng = StdRng::seed_from_u64(s);```
```auto s = 8;
auto gen = Random(s);
writeln(gen.front);```
70
Get the current datetime and provide it as a seed to a random generator. The generator sequence will be different at each run.
`rand = random.Random()`
```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());```
`auto rng = Random(cast(uint)Clock.currTime.stdTime);`
Alternative implementation:
`rndGen.seed(cast(uint)Clock.currTime.stdTime);`
71
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.
`print ' '.join(sys.argv[1:])`
`println!("{}", env::args().skip(1).collect::<Vec<_>>().join(" "));`
Alternative implementation:
`println!("{}", std::env::args().skip(1).format(" "));`
```void main(string[] args)
{
args[1..\$].join(" ").writeln;
}```
Alternative implementation:
```void main(string[] args)
{
writeln(args.dropOne.joiner(" "));
}```
73
Create a factory named fact for any sub class of Parent and taking exactly one string str as constructor parameter.
```def fact(a_class, str_):
if issubclass(a_class, Parent):
return a_class(str_)```
```auto fact(T, A...)(A a)
if (is(T==class) && is(T: Parent))
{
return new T(a);
}```
74
Compute the greatest common divisor x of big integers a and b. Use an integer type able to handle huge numbers.
`x = gcd(a, b)`
`let x = a.gcd(&b);`
`x = gcd(a, b);`
Alternative implementation:
```BigInt gcd(in BigInt x, in BigInt y) pure {
if (y == 0)
return x;
return gcd(y, x%y);
}

gcd(a, b);```
75
Compute the least common multiple x of big integers a and b. Use an integer type able to handle huge numbers.
`x = (a*b)//gcd(a, b)`
`let x = a.lcm(&b);`
`uint x = (a * b) / gcd(a, b);`
76
Create the string s of integer x written in base 2.

E.g. 13 -> "1101"
`s = '{:b}'.format(x)`
`let s = format!("{:b}", x);`
`auto s = to!string(x,2);`
77
Declare a complex x and initialize it with value (3i - 2). Then multiply it by i.
```x = 3j-2
y = x * 1j```
```let mut x = Complex::new(-2, 3);
x *= Complex::i();```
```auto x = complex(-2, 3);
x * complex(0, 1);```
78
Execute a block once, then execute it again as long as boolean condition c is true.
```while True:
do_something()
if not c:
break```
```loop {
doStuff();
if !c { break; }
}```
```do
{
something;
somethingElse;
}
while (c);```
79
Declare floating point number y and initialize it with the value of integer x .
`y = float(x)`
`let y = x as f32;`
```int x;
float y = to!float(x);
// or
float y = cast(float) x;```
80
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;`
`int y = cast(int)x;`
81
Declare integer y and initialize it with the rounded value of floating point number x .
Ties (when the fractional part of x is exactly .5) must be rounded up (to positive infinity).
`y = int(x + 0.5)`
`let y = x.round() as i64;`
`int y = cast(int) x.round;`
82
Find how many times string s contains substring t.
Specify if overlapping occurrences are counted.
`count = s.count(t)`
`let c = s.matches(t).count();`
`auto occurrences = s.count(t);`
83
Declare regular expression r matching strings "http", "htttp", "httttp", etc.
`r = re.compile(r"htt+p")`
`let r = Regex::new(r"htt+p").unwrap();`
`auto r = regex("htt+p");`
84
Count number c of 1s in the integer i in base 2.

E.g. i=6 → c=2
`c = bin(i).count("1")`
`let c = i.count_ones();`
`auto c = bitSet(i).length;`
85
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.
```def adding_will_overflow(x,y):
return False```
```fn adding_will_overflow(x: usize, y: usize) -> bool {
x.checked_add(y).is_none()
}```
```bool addingWillOverflow(int x, int y)
{
bool result;
core.checkedint.adds(x, y, result);
return result;
}```
86
Write boolean function multiplyWillOverflow 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.
```def multiplyWillOverflow(x,y):
return False```
```fn multiply_will_overflow(x: i64, y: i64) -> bool {
x.checked_mul(y).is_none()
}```
```bool multiplyWillOverflow(int x, int y)
{
bool result;
core.checkedint.muls(x, y, result);
return result;
}```
87
Exit immediatly.
If some extra cleanup work is executed by the program runtime (not by the OS itself), describe it.
`sys.exit(1)`
`std::process::exit(0);`
`exit(0);`
88
Create a new bytes buffer buf of size 1,000,000.
`buf = bytearray(1000000)`
`let buf: Vec<u8> = Vec::with_capacity(1000000);`
`void[] buf = malloc(1024 * 1024)[0..1024 * 1024];`
Alternative implementation:
`void[] buf = GC.malloc(1024 * 1024)[0..1024 * 1024];`
89
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.
`raise ValueError("x is invalid")`
```enum CustomError { InvalidAnswer }

fn do_stuff(x: i32) -> Result<i32, CustomError> {
if x != 42 {
Err(CustomError::InvalidAnswer)
} else {
Ok(x)
}
}```
`throw new Exception("invalid value for x (%s) in '%s'".format(x, __PRETTY_FUNCTION__));`
Alternative implementation:
```void foo(int x)
in
{
assert(x != 0, "wrong value for x");
}
body
{
// function
}```
90
Expose a read-only integer x to the outside world while being writable inside a structure or a class Foo.
```class Foo(object):
def __init__(self):
self._x = 0

@property
def x(self):
"""
Doc for x
"""
return self._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;
}
}```
```struct Foo
{
private int _x;
int x() {return _x;}
}```
91
Read from file data.json and write its content into object x.
Assume the JSON data is suitable for the type of x.
```with open("data.json", "r") as input:
x = json.load(input)```
`let x = ::serde_json::from_reader(File::open("data.json")?)?;`
```JSONValue x = "data.json".readText.parseJSON;

struct User {
int age;
string name;

this(JSONValue user) {
age  = user["age"];
name = user["name"];
}
}

auto user = User(x);```
92
Write content of object x into file data.json.
```with open("data.json", "w") as output:
json.dump(x, output)```
`::serde_json::to_writer(&File::create("data.json")?, &x)?`
```auto x = JSONValue(["age":42, "name":"Bob"]);
"data.json".write(x.toJSON);```
93
Implement procedure control which receives one parameter f, and runs f.
```def control(f):
return f()```
```fn control(f: impl Fn()) {
f();
}```
```void control(alias f)()
if (isCallable!f)
{
f();
}```
Alternative implementation:
```void control(void function() f)
{
f();
}```
94
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.
`print(type(x))`
Alternative implementation:
`print(x.__class__)`
```fn type_of<T>(_: &T) -> &'static str {
std::intrinsics::type_name::<T>()
}

println!("{}", type_of(&x));```
`writeln(typeid(x));`
95
Assign to variable x the length (number of bytes) of the local file at path.
`x = os.path.getsize(path)`
`let x = fs::metadata(path)?.len();`
Alternative implementation:
`let x = path.metadata()?.len();`
`auto x = getSize(path);`
96
Set boolean b to true if string s starts with prefix prefix, false otherwise.
`b = s.startswith(prefix)`
`let b = s.starts_with(prefix);`
`b = s.startsWith(prefix);`
97
Set boolean b to true if string s ends with string suffix, false otherwise.
`b = s.endswith(suffix)`
`let b = s.ends_with(suffix);`
`b = s.endsWith(suffix);`
98
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 = datetime.date.fromtimestamp(ts)`
`let d = NaiveDateTime::from_timestamp(ts, 0);`
`auto d = SysTime(unixTimeToStdTime(ts), UTC());`
99
Assign to string x the value of fields (year, month, day) of date d, in format YYYY-MM-DD.
```d = date(2016, 9, 28)
x = d.strftime('%Y-%m-%d')```
Alternative implementation:
```d = date.today()
x = d.isoformat()```
`Utc::today().format("%Y-%m-%d")`
`string x = Date(1993, 10, 26).toISOExtString;`
100
Sort elements of array-like collection items, using a comparator c.
`items.sort(c)`
`items.sort_by(c);`
`items.sort!c;`
101
Make an HTTP request with method GET to URL u, then store the body of the response in string s.
```with urllib.request.urlopen(u) as f:
s = f.read()
```
```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)?;```
`string s = u.get.to!string;`
102
Make an HTTP request with method GET to URL u, then store the body of the response in file result.txt. Try to save the data as it arrives if possible, without having all its content in memory at once.
```filename, headers = urllib.request.urlretrieve(u, 'result.txt')
```
```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),
};```
`u.download("result.txt");`
103
Read from file data.xml and write its content into object x.
Assume the XML data is suitable for the type of x.
`x = lxml.etree.parse('data.xml')`
```XmlArchive archive = new XmlArchive!(char);
archive.doc.parse(read("data.xml"));
Serializer ser = new Serializer(archive);
ser.deserialize(x);```
104
Write content of object x into file data.xml.
```# Python 2.5 to 2.7
# Use pickle or marshall module
class TestClass(object):
a = None
b = None
c = None

def __init__(self, a, b, c):
self.a = a
self.b = b
self.c = c

tst = TestClass("var_a", "var_b", "var_c")
ser = pyx.serialize(obj=tst, enc="utf-8")
print(ser)```
```auto archive = new XmlArchive!(char);
auto serializer = new Serializer(archive);
serializer.serialize(x);
write("data.xml", archive.data);```
105
Assign to string s the name of the currently executing program (but not its full path).
`s = sys.argv`
```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();```
```void main(string[] args) {
string s = args.baseName;
}```
106
Assign to string dir the path of the working directory.
(This is not necessarily the folder containing the executable itself)
`dir = os.getcwd()`
`let dir = env::current_dir().unwrap();`
`string dir = absolutePath;`
107
Assign to string dir the path of the folder containing the currently running executable.
(This is not necessarily the working directory, though.)
`dir = os.path.dirname(os.path.abspath(__file__))`
```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();```
```void main(string[] args) {
string dir = args.dirName;
}```
108
Print the value of variable x, but only if x has been declared in this program.
This makes sense in some languages, not all of them. (Null values are not the point, rather the very existence of the variable.)
```if 'x' in locals():
print x```
```int x = 42;

void printIfDefined(alias name)()
{
import std.stdio: writeln;
static if( __traits(compiles, writeln(mixin(name))))
writeln(mixin(name));
}

void main(string[] args)
{
printIfDefined!"x";
printIfDefined!"Foo.bar";
}```
Alternative implementation:
```static if (is(typeof(x = x.init)))
writeln(x);```
109
Set n to the number of bytes of a variable t (of type T).
`n = pympler.asizeof.asizeof(t)`
`let n = ::std::mem::size_of::<T>();`
`auto n = T.sizeof;`
110
Set boolean blank to true if string s is empty, or null, or contains only whitespace ; false otherwise.
`blank = s is None or s.strip() == ''`
`let blank = s.trim().is_empty();`
`bool blank = s.all!isSpace;`
111
From current process, run program x with command-line parameters "a", "b".
`subprocess.call(['x', 'a', 'b'])`
```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");```
`spawnProcess([x, "a", "b"]);`
112
Print each key k with its value x from an associative array mymap, in ascending order of k.
```for k in sorted(mymap):
print(mymap[k])
```
```for (k, x) in mymap {
println!("({}, {})", k, x);
}```
```mymap.byKeyValue
.array
.sort!((a, b) => a.key < b.key)
.each!(p => writeln(p.key, " ", p.value));
```
113
Print each key k with its value x from an associative array mymap, in ascending order of x.
Note that multiple entries may exist for the same value x.
```for x, k in sorted((x, k) for k,x in mymap.items()):
print(k, 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);
}```
```mymap.byKeyValue
.array
.sort!((a, b) => a.value < b.value)
.each!(p => writeln(p.key, " ", p.value));
```
114
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 = x == y`
`let b = x == y;`
`b = deeplyEqual(x, y));`
115
Set boolean b to true if date d1 is strictly before date d2 ; false otherwise.
`b = d1 < d2`
`let b = d1 < d2;`
`bool b = d1 < d2;`
116
Remove all occurrences of string w from string s1, and store the result in s2.
`s2 = s1.replace(w, '')`
`s2 = s1.replace(w, "");`
Alternative implementation:
`let s2 = str::replace(s1, w, "");`
`auto s2 = s1.replace(w, "");`
117
Set n to the number of elements of list x.
`n = len(x)`
```let n = x.len();

```
`auto n = x.length;`
Alternative implementation:
`n = walkLength(x);`
118
Create set y from list x.
x may contain duplicates. y is unordered and has no repeated values.
`y = set(x)`
`let y: HashSet<_> = x.into_iter().collect();`
```bool[typeof(x)] y;

foreach (e ; x)
y[e] = true;```
Alternative implementation:
`auto y = redBlackTree(x);`
119
Remove duplicates from list x.
Explain if original order is preserved.
`x = list(set(x))`
Alternative implementation:
`x = list(OrderedDict(zip(x, x)))`
```x.sort();
x.dedup();```
Alternative implementation:
`let dedup: Vec<_> = x.iter().unique().collect();`
`x = x.sort.uniq.array;`
Alternative implementation:
`x = redBlackTree(x)[].array;`
120
Read an integer value from the standard input into variable n
`n = int(input("Input Prompting String: "))`
```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");```
`readf("%d", &n);`
121
Listen UDP traffic on port p and read 1024 bytes into buffer b.
```sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind((UDP_IP, p))
while True:
data, addr = sock.recvfrom(1024)
print("received message:", data)```
```let mut b = [0 as u8; 1024];
let sock = UdpSocket::bind(("localhost", p)).unwrap();
sock.recv_from(&mut b).unwrap();```
```ubyte b;

auto sock = new UdpSocket();
scope(exit) sock.close;

sock.bind(new InternetAddress(p));
sock.receive(b);```
122
Create an enumerated type Suit with 4 possible values SPADES, HEARTS, DIAMONDS, CLUBS.
```class Suit:
SPADES, HEARTS, DIAMONDS, CLUBS = range(4)```
Alternative implementation:
```class Suit(Enum):
SPADES = 1
HEARTS = 2
DIAMONDS = 3
CLUBS = 4```
```enum Suit {
Spades,
Hearts,
Diamonds,
Clubs,
}```
```enum Suit{
SPADES,
HEARTS,
DIAMONDS,
CLUBS
}```
123
Verify that predicate isConsistent returns true, otherwise report assertion violation.
Explain if the assertion is executed even in production environment or not.
`assert isConsistent`
`assert!(is_consistent);`
`assert(isConsistent);`
124
Write function binarySearch which returns the index of an element having value x in sorted array a, or -1 if no such element.
```def binarySearch(a, x):
i = bisect.bisect_left(a, x)
return i if i != len(a) and a[i] == x else -1
```
`a.binary_search(&x).unwrap_or(-1);`
```long binarySearch(long[] a, long x) {
long result = a.assumeSorted.lowerBound(x).length;
if (result == a.length || a[result] != x)
return -1;
return result;
}```
125
measure the duration t, in nano seconds, of a call to the function foo. Print this duration.
```t1 = time.perf_counter()
foo()
t2 = time.perf_counter()
print('Seconds:', t2 - t1)```
```let start = Instant::now();
foo();
let duration = start.elapsed();
println!("{}", duration);
```
```StopWatch sw;
sw.start;
foo;
auto t = sw.peek.nsecs;
writeln(t);
```
126
Write a function foo that returns a string and a boolean value.
```def foo():
return 'string', True
```
```fn foo() -> (String, bool) {
(String::from("bar"), true)
}```
```auto foo()
{
return tuple("theString", true);
}```
127
Import the source code for the function foo body from a file "foobody.txt" . The declaration must not reside in the external file.
`foo = imp.load_module('foobody', 'foobody.txt').foo`
```fn main() {
include!("foobody.txt");
}
```
```void foo()
{
mixin(import("foobody.txt"));
}```
128
Call a function f on every node of a tree, in breadth-first prefix order
```def BFS(f, root):
Q = [root]
while Q:
n = Q.pop(0)
f(n)
for child in n:
if not n.discovered:
n.discovered = True
Q.append(n)```