goofballLogic

const replaceRepeats = (input, number) => 
    input.replaceAll(
        new RegExp(`${number}+`, "g"), 
        x => x.length);

// test

[
    replaceRepeats('1234500362000440', 0) === "1234523623441",
    replaceRepeats('000000000000', 0) == "12",

goofballLogic

/* solution */

const validate = ([y, z, ...rest]) =>
    rest.length
        ? (rest.shift() === y && validate([z, y, ...rest]))
        : true;



/* testing */

goofballLogic

/* solution */

function process([y, z, ...rest] = []) {
    while (rest.length) {
        if (rest.shift() !== y) return false;
        [z, y] = [y, z];
    }
    return true;
}    

goofballLogic

const rotate = ([ head, ...tail]) => [...tail, head];
const explode = (num, acc = []) => 
    num === 0 ? acc 
    : explode(num - 1, [num, ...acc])
    ; 
const build = (num, input, lines = []) => 
    num === 0 ? lines 
    : build(num - 1, rotate(input), [...lines, input])
    ;

goofballLogic

// below here we can use functional structures again

const suits = ["♠", "♥", "♣", "♦"];
const cards = ["A", "K", "Q", "J", "9", "8", "7", "6", "5", "4", "3", "2"];

function new_deck() {
    return suits.flatMap(suit => 
        cards.map(card => `${card}${suit}`));
}

goofballLogic

const maybeAdd = (prev, candidate) =>
  prev.endsAt <= candidate[1]
    ? [prev, { 
        chosen: [...prev.chosen, candidate[0]],
        endsAt: candidate[2]
    }]
    : [prev];

const combine = ts =>
  ts.reduce(

goofballLogic

const taskListEndsAt = ts => 
  Math.max(...ts.map(t => t[2]));

const maybeAdd = (ts, candidate) => 
  (taskListEndsAt(ts) <= candidate[1])
    ? [ts, [...ts, candidate]]
    : [ts]
    ;

const combinations = ts => 

goofballLogic

function repeatedIntegers_0(n) {
    const ret = []; 
    for(let i = 0; i <= n; i++)
        ret.push(...String(i).repeat(i).split("").map(i => Number(i)));
    return ret;
}

function* repeatedIntegers_1(n) {
    let i = 0;
    while(++i <= n)

goofballLogic

// Set up:
//  - dotnet new console
//  - dotnet add package OneOf

// Implement each of the methods below so that they all compile
// There only one valid implementation for each function (apart from f5 & f6)

using OneOf;

A F1<A>(A a) {

goofballLogic

class Cat {
  speak() { return "meow"; }
}

function process(cat) { 
  return cat.speak(); 
}

class Ball {
}