#modular-arithmetic code explainers

javascript

const IBAN_LENGTHS = {
  DE: 22, FR: 27, GB: 22, ES: 24, IT: 27,
  NL: 18, BE: 16, CH: 21, AT: 20, PT: 25,
};

How IBAN validation works in JavaScript

validation checksum modular-arithmetic

Intermediate 8 steps

typescript

export function isValidCardNumber(input: string): boolean {
  const digits = input.replace(/[\s-]/g, "");
 
  if (!/^\d{12,19}$/.test(digits)) {

Validating card numbers with the Luhn check

luhn-algorithm checksum input-validation

Intermediate 7 steps

javascript

function generateCalendarGrid(year, month) {
  const firstDay = new Date(year, month, 1);
  const lastDay = new Date(year, month + 1, 0);
  const daysInMonth = lastDay.getDate();

Building a text calendar in JavaScript

date-handling grid-layout modular-arithmetic

Intermediate 9 steps

java

public final class IbanValidator {
 
    private static final Map<String, Integer> COUNTRY_LENGTHS = Map.ofEntries(
        Map.entry("DE", 22), Map.entry("FR", 27), Map.entry("GB", 22),

Validating IBANs with the mod-97 checksum

validation checksum modular-arithmetic

Intermediate 8 steps

ruby

module DurationFormatter
  UNITS = [
    ['week', 604_800],
    ['day', 86_400],

Turning seconds into human-readable durations in Ruby

greedy-decomposition modular-arithmetic formatting

Intermediate 7 steps