Berlin Clock Kata
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Round light blinks to denote odd (on) or even (off) seconds.
1st row denotes five full hours each. 2nd row denotes one hour each.
3rd row eleven lights, which denote five full minutes each.
4th row indicates one full.

Kata

A code kata is an exercise in programming which helps programmers hone their skills through practice and repetition.

Theme of the day

Purely functional style.

Constraints

Only const, no let.
No re-assignment or mutation.
Recursion for iteration.
Avoid built-ins.

No re-assignment

array[0] = 1;
object.x = 2;

No mutation

Given this

const a = [1, 2, 3];

None of this

a.push(4);
a.reverse();
a.sort()
a.splice(1, 3);

Destruct & construct

function withFirst(x, array) {
  const [_, ...rest] = array;
  return [x, ...rest];
}

function withKey(object, key, value) {
  return { ...object, [key]: value };
}

Recursion to iterate

No for, while, or .forEach.

a.map(n => n + 1);
a.filter(n => n % 2);
a.reduce((acc, n) => acc + n);

function range(n, m) {
  return Array.from({length: m - n})
    .map((_, index) => n + index);
}

Bonus: avoid built-ins

Replace .map, .reduce, .slice(1).

function tail(xs) {
  const [, ...rest] = xs;
  return rest;
}

function reduce(fn, xs, acc) {
  return xs.length > 0
    ? reduce(fn, tail(xs), fn(acc, xs[0]))
    : acc;
}

function map(fn, xs) {
  return reduce((acc, x) => [...acc, fn(x)], xs, []);
}

Without Array.from.

function range(n, m) {
  return n < m ? [n, ...range(n + 1, m)] : [];
}

Specification

          S H×5  H    M×5         M
00:00:00  . .... .... ........... ....
00:00:01  X .... .... ........... ....
22:23:18  . XXXX XX.. XX|X....... XXX.

Template

require('readline')
  .createInterface({ input: process.stdin })
  .on('line', line => console.log(`${line} => ${toBerlinClock(line)}`));

function toBerlinClock(line) {
  return '. .... .... ........... ....';
}

$ echo 10:15:00 | node main.js
10:15:00 => . XX.. .... XX|........ ....
$ node main.js < example.txt
00:00:00 => . .... .... ........... ....
23:59:59 => X XXXX XXX. XX|XX|XX|XX XXXX
18:48:02 => . XXX. XXX. XX|XX|XX|.. XXX.

Berlin Clock Kata Wix Grow Activity

Berlin Clock Kata
Wix Grow Activity