JavaScript Collection of solved tasks from the codewars site

There will be examples of solutions, I do not recommend using the offered code to solve your tasks. I want to warn you that if you try to use the answers shown, you are likely to be blocked by the site. The repository was created primarily as a collection of examples for possible study, and help newcomers.

Kata

8 - kyu
7 - kyu
6 - kyu
5 - kyu
4 - kyu
3 - kyu
2 - kyu
1 - kyu

8 Kyu

Heads and Legs | 8 kyu | ⬆️UP

function animals(heads, legs){
  for(var i = 0; i <= heads; i++){
    if( (i * 4 + (heads- i) * 2) == legs){
      return [heads- i,i];
    }
  }
  return 'No solutions';
}

Hello, Name or World! | 8 kyu | ⬆️UP

const hello = name => return `Hello, ${name ? name.at(0).toUpperCase() + name?.slice(1).toLowerCase() : 'World'}!`

A Strange Trip to the Market | 8 kyu | ⬆️UP

const isLockNessMonster = s => s.includes('tree fiddy') || s.includes('3.50') || s.includes('three fifty')

Add new item (collections are passed by reference) | 8 kyu | ⬆️UP
```
const addExtra = listOfNumbers => [...listOfNumbers,'cock']
```
Exclamation marks series #4: Remove all exclamation marks from sentence but ensure a exclamation mark at the end of string | 8 kyu | ⬆️UP
```
const remove = string => string.replace(/!/g, '') + '!'
```
Exclamation marks series #2: Remove all exclamation marks from the end of sentence | 8 kyu | ⬆️UP
```
const remove = s => s.replace(/!+$/, '');
```

Grasshopper - Variable Assignment Debug | 8 kyu | ⬆️UP

var a = "dev"
var b = "Lab"

var name = a + b

Return Two Highest Values in List | 8 kyu | ⬆️UP

const twoHighest = arr => [...new Set(arr)].sort((a,b) => a-b).slice(-2).reverse()

How old will I be in 2099? | 8 kyu | ⬆️UP

const calculateAge = (m, n) => {
  if(m == n) return 'You were born this very year!';

  const year = Math.abs(m-n) == 1 ? 'year' : 'years';

  if(m < n) return "You are "+(n-m)+' '+year+' old.';
  if(m > n) return "You will be born in "+(-n+m)+' '+year+'.';
}

Ensure question | 8 kyu | ⬆️UP

const ensureQuestion = s => s.endsWith('?') ? s : s + '?'

Total pressure calculation | 8 kyu | ⬆️UP

function solution(M1, M2, m1, m2, V, T) {
		M1 = m1 * 0.001/M1;
    M2 = m2 * 0.001/M2;
    T = T + 273.15;
	  const R = 0.082;

	  return (((M1 + M2) * R * T) / V) * 1000;
}

Enumerable Magic #1 - True for All? | 8 kyu | ⬆️UP
```
const all = ( arr, fun ) => arr.every(fun)
```

Parse float | 8 kyu | ⬆️UP

const parseF = s =>  isNaN(parseFloat(s)) ? null : parseFloat(s)

SpeedCode #2 - Array Madness | 8 kyu | ⬆️UP

const arrayMadness = (a, b) => a.reduce((acc, x) => acc + x**2, 0) > b.reduce((acc, x) => acc + x**3, 0)

easy logs | 8 kyu | ⬆️UP

const logs = (x , a, b) =>  (Math.log(a*b) / Math.log(x))

Classy Classes | 8 kyu | ⬆️UP

class Person {

  constructor(name, age) {
    this.name = name;
    this.age = age;
  }
  
  get info() {
    return `${this.name}s age is ${this.age}`;
  }
}

Pole Vault Starting Marks | 8 kyu | ⬆️UP

const startingMark = bodyHeight => +(bodyHeight * 3.9354 + 3.4681).toFixed(2);

Training JS #6: Basic data types--Boolean and conditional statements if..else | 8 kyu | ⬆️UP
```
const trueOrFalse =(val) => Boolean(val).toString()
```

Fuel Calculator: Total Cost | 8 kyu | ⬆️UP

function fuelPrice(litres, pricePerLiter) {
  var discount = Math.min(Math.floor(litres/2) * 0.05, 0.25);
  var price = litres * (pricePerLiter - discount);
  return Math.round(price*100) / 100;
}

Days in the year | 8 kyu | ⬆️UP

const yearDays = year => `${year} has 36${6 - !!(year % 400 && !(year % 100) || year % 4)} days`;

Arguments to Binary addition | 8 kyu | ⬆️UP

const arr2bin = arr => arr.filter(x => typeof x == 'number').reduce((x, y) => x + y, 0).toString(2);

Training JS #34: methods of Math---pow() sqrt() and cbrt() | 8 kyu | ⬆️UP

function cutCube(volume,n){
  return !(Math.cbrt(n) % 1) && !(Math.cbrt(volume / n) % 1);
}

Training JS #17: Methods of String object--indexOf(), lastIndexOf() and search() | 8 kyu | ⬆️UP

const firstToLast = (str,c) => (str.indexOf(c) < 0) ? -1 : str.lastIndexOf(c) - str.indexOf(c)

Implement Array.prototype.filter() | 8 kyu | ⬆️UP

Array.prototype.filter = function (func) {
  const result = []
  this.forEach(el => func(el) ? result.push(el) : null)      
  return result
}

Job Matching #1 | 8 kyu | ⬆️UP

function match(candidate, job) {
    if(!candidate.minSalary || !job.maxSalary) throw "Error!!";
    return (candidate.minSalary * 0.9) <= job.maxSalary;
}

Lexical this | 8 kyu | ⬆️UP

 var Person = function(){
    var person = {
      _name: "Leroy",
      _friends: [],
      fillFriends(f){
        this._friends.push(...f);
      }
    }
    return person;
}

7 Kyu

ASCII letters from Number | 7 kyu | ⬆️UP

function convert(number){
  const arr = []
  
  for(let i = 0; i < number.length; i+=2){
    arr.push(String.fromCharCode(number.substr(i,2)))
  }
  
  return arr.join('')
 }

Find the next perfect square! | 7 kyu | ⬆️UP

function findNextSquare(sq) {
  return Math.sqrt(sq)%1? -1 : Math.pow(Math.sqrt(sq)+1,2);
}

Ones and Zeros | 7 kyu | ⬆️UP

const binaryArrayToNumber = arr => {
  return parseInt(arr.join(""), 2)
};

Sum of the first nth term of Series | 7 kyu | ⬆️UP

function SeriesSum(n) {
  var sum = 0;
  for(var i = 0; i < n; i++) {
    sum += 1 / (3 * i + 1);
  }
  return sum.toFixed(2);
}

Sort array by string length | 7 kyu | ⬆️UP

 let sortByLength = arr => arr.sort((a,b) => a.length - b.length);

Find the middle element | 7 kyu | ⬆️UP

 const gimme = function (arr) {
    return arr.indexOf([...arr].sort((x, y) => x > y)[1]);
 };

Round up to the next multiple of 5 | 7 kyu | ⬆️UP

 function roundToNext5(n){
    return Math.ceil(n/5)*5;
  }

Simple Fun #176: Reverse Letter | 7 kyu | ⬆️UP

 function reverseLetter(str) {
    return str.replace(/[^a-z]/gi,'').split('').reverse().join('')  
}

Summing a number's digits | 7 kyu | ⬆️UP

function sumDigits(number) {
  return `${Math.abs(number)}`.split('').reduce((acc,el) => acc + +el,0)
}

Check the exam | 7 kyu | ⬆️UP

function checkExam(array1, array2) {
  let result = 0;
  
  for(let i in array1){
    if(array2[i] === '') continue;
    array1[i] === array2[i] ? result+=4 : result-=1;
  }
  
  return Math.max(result,0)
}

Fix string case | 7 kyu | ⬆️UP

function solve(s){
    return s.match(/[a-z]/g).length >= s.length / 2 ? s.toLowerCase() : s.toUpperCase()
}

Triangular Treasure | 7 kyu | ⬆️UP

function triangular( n ) {
  return n > 0 ? n * (n + 1) / 2 : 0;
}

Most digits | 7 kyu | ⬆️UP

const findLongest = l => l.reduce((a, b) => (`${b}`.length > `${a}`.length) ? b : a);

Reverse a Number 7 kyu | ⬆️UP

const reverseNumber = n => (n > 0 ? 1 : -1) * Math.abs(n).toString().split('').reverse().join('')

Minimize Sum Of Array (Array Series #1) | ⬆️UP

function minSum(arr) {
  const l = arr.length;
  const sorted = arr.sort((a, b) => b - a);
  const max = sorted.slice(0, l/2);
  const min = sorted.slice(l/2, l).reverse();
  
  return max.reduce((sum, el, i) => sum + el * min[i], 0);
}

Moves in squared strings (I) | ⬆️UP

const vertMirror = s => s.map(s => [...s].reverse().join(''));
const horMirror = s => s.reverse();

const oper = (fct, s) => fct(s.split("\n")).join("\n");

All unique | ⬆️UP

let hasUniqueChars = (str) => new Set(str).size === str.length;

Palindrome chain length | ⬆️UP

const palindromeChainLength = n => {
  let count = 0;

  while(+[...`${n}`].reverse().join('') !== n){
    n+= +[...`${n}`].reverse().join('')
    count++;
  }
  
  return count
};

Speed Control | ⬆️UP

const gps = (s, x) => {

  if (x.length<=1) {
    return 0;
  }
  
  let output = [];
  for (let i = 0; i < x.length-1; i++) { 
    output.push((x[i+1]-x[i])*3600/s);
  }
  
  return Math.max(...output);
}

Coding Meetup #2 - Higher-Order Functions Series - Greet developers | ⬆️UP

 const greetDevelopers = list => list.map(dev => ({...dev, greeting: `Hi ${dev.firstName}, what do you like the most about ${dev.language}?`}));

Halving Sum | ⬆️UP

 const halvingSum = n => n > 1 ? n + halvingSum(n / 2 | 0) : n

max diff - easy | ⬆️UP

 function maxDiff(list) {
   return list.length ? Math.max(...list) - Math.min(...list) : 0;
 };

Over The Road | 🌐Source | ⬆️UP

 function maxDiff(list) {
   return list.length ? Math.max(...list) - Math.min(...list) : 0;
 };

Simple beads count | 🌐Source | ⬆️UP

 function countRedBeads(n) {
   return n < 2 ? 0 : 2 * n - 2;
 }

Boiled Eggs | 🌐Source | ⬆️UP

function cookingTime(eggs) {
  return 5 * Math.ceil(eggs / 8);
}

Simple remove duplicates | 🌐Source | ⬆️UP

 function solve(arr){
   return arr.filter((val,i) => arr.lastIndexOf(val) == i);
 }

Find the nth Digit of a Number | 🌐Source | ⬆️UP

var findDigit = function(num, nth){
  if(nth <= 0) return -1
  num = `${Math.abs(num)}`
  
  return num.length >= nth ? +num.at(num.length - nth) : 0
}

esreveR | 🌐Source | ⬆️UP

 reverse = function(array) {
   return array.map((c, i) => array[array.length - 1 - i]);
 }

Sum of array singles | 🌐Source | ⬆️UP

 function repeats(arr){
   return arr.reduce((acc,el) => arr.indexOf(el) === arr.lastIndexOf(el) ? acc+=el : acc,0)
 };

Gauß needs help! (Sums of a lot of numbers). | 🌐Source | ⬆️UP

 function f(n){
   if(typeof n !== 'number' || !Number.isInteger(n) || n <= 0) return false
   return ((1 + n)*n)/2
 };

Alphabetical Addition | 🌐Source | ⬆️UP

function addLetters(...letters) {
  const alpha = 'zabcdefghijklmnopqrstuvwxy';
  const sum = letters.reduce((sum, letter) => sum + alpha.indexOf(letter), 0) % 26;
  return alpha[sum];
}

Filter the number | 🌐Source | ⬆️UP

const FilterString = value => +value.replace(/\D/g, '');

Simple Fun #74: Growing Plant | 🌐Source | ⬆️UP

function growingPlant(upSpeed, downSpeed, desiredHeight) {
  let count = 0, height = 0;
  while(true){
    count++;
    height+=upSpeed;
    if(height >= desiredHeight) return count;
    height-=downSpeed;
  }
}

Coloured Triangles | 🌐Source | ⬆️UP

function triangle(row) {
  let result = ''
  if(row.length == 1) result = row;
  
  for(let i = 0; i < row.length - 1; i++){
    if(row[i] === row[i+1]) result+= row[i]
    else result+= 'RGB'.replace(row[i],'').replace(row[i+1],'')
  }
  
  if(row.length > 1) return triangle(result)
  else return result
}

Strong Number (Special Numbers Series #2) | 🌐Source | ⬆️UP

function strong(n) {
  return [1,2,145,40585].includes(n) ? 'STRONG!!!!' : 'Not Strong !!'
}

Help the Fruit Guy | 🌐Source | ⬆️UP

function removeRotten(arr){
  return arr ? arr.map(x=>x.replace('rotten', '').toLowerCase()) : [] ;
}

Currying functions: multiply all elements in an array | 🌐Source | ⬆️UP
```
const multiplyAll = arr => n => arr.map(x => n * x);
```

Alternate case | 🌐Source | ⬆️UP

function alternateCase(s) {
  return [...s].map(el => el === el.toLowerCase() ? el.toUpperCase() : el.toLowerCase()).join('')
}

Basic Calculator | 🌐Source | ⬆️UP

function calculate(num1, operation, num2) {
  var ops = {
    '+': function(x, y) { return x + y; },
    '-': function(x, y) { return x - y; },
    '*': function(x, y) { return x * y; },
    '/': function(x, y) { return y === 0 ? null : x / y; }
  };
  return (ops[operation] || function() { return null; })(num1, num2);
}

Disarium Number (Special Numbers Series #3) | 🌐Source | ⬆️UP

function disariumNumber(n){
  return [...`${n}`].reduce((acc,el,i) => acc+=el**(i+1),0) === n ? 'Disarium !!' : 'Not !!'
}

Building blocks | 🌐Source | ⬆️UP

class Block{

  constructor(data){
    [this.width, this.length, this.height] = data;
  }
  
  getWidth() {
    return this.width;
  }
  
  getLength() {
    return this.length;
  }
  
  getHeight() {
    return this.height;
  }
  
  getVolume() {
    return this.width * this.length * this.height;
  }
  
  getSurfaceArea () {
    return 2 * (this.width * this.length + this.width * this.height + this.length * this.height);
  }
}

SevenAte9 | 🌐Source | ⬆️UP

function sevenAte9(str){
  return str.replace(/79(?=7)/g, '7');
}

Difference Of Squares | 🌐Source | ⬆️UP

function differenceOfSquares(n){
  const arr = Array.from({length:n}, (_,i) => i+1)
  return arr.reduce((acc,el) => acc+el,0)**2 - arr.reduce((acc,el) => acc+=el**2,0)
}

Digital cypher | 🌐Source | ⬆️UP

function encode(str,  n){
  return  [...str].map((el,i) => (el.charCodeAt() - 96) + +`${n}`.at(i%`${n}`.length))
}

Return the closest number multiple of 10 | 🌐Source | ⬆️UP

const closestMultiple10 = num => Math.round(num / 10) * 10;

Substituting Variables Into Strings: Padded Numbers | 🌐Source | ⬆️UP

function solution(value){
  return "Value is " + ("00000" + value).slice(-5);
}

The old switcheroo | 🌐Source | ⬆️UP

function vowel2index(str) {
   return str.replace(/[aeiou]/ig, (m, i) => i + 1);
}

Word values | 🌐Source | ⬆️UP

function wordValue(a) {
	return a.map((el,i) => el.replace(/ /g, '').split('').reduce((acc,letter) => acc+letter.charCodeAt() - 96,0) * (i+1))
}

Convert a linked list to a string | 🌐Source | ⬆️UP

function stringify(list) {
	return list === null ? "null" : `${list.data} -> ${stringify(list.next)}`; 
}

ToLeetSpeak | 🌐Source | ⬆️UP

const toLeetSpeak = s => s.replace(/[ABCEGHILOSTZ]/g, c => D[c]);

Split In Parts | 🌐Source | ⬆️UP

var splitInParts = function(s, partLength){
  let result = []
  
  for(let i = 0; i < s.length; i+=partLength){
    result.push(s.substr(i,partLength))
  }
  
  return result.join(' ')
}

Valid Spacing | 🌐Source | ⬆️UP

function validSpacing(s) {
  return s.trim() == s && !s.includes("  ");
}

Count all the sheep on farm in the heights of New Zealand | 🌐Source | ⬆️UP

const lostSheep = (f,s,n) => n - [...f,...s].reduce((a,b) => a + b,0)

Insert dashes | 🌐Source | ⬆️UP

function insertDash(num) {
  let result = ''
  num = `${num}`
  for(let i = 0; i < num.length; i++){
    if(num[i]&1 && num[i+1]&1) result+=`${num[i]}-`
    else result+=num[i]
  }
  
  return result
}

Band name generator | 🌐Source | ⬆️UP

function bandNameGenerator(str) {
  return str.at(0) !== str.at(-1) ? `The ${str.at(0).toUpperCase() + str.slice(1)}` : `${str.charAt(0).toUpperCase() + str.slice(1) + str.slice(1)}`
}

Arithmetic progression | 🌐Source | ⬆️UP

function arithmeticSequenceElements(a, r, n) {
  return Array.from({length: n}, (_, i) => a + r * i).join(', ');
}

Stanton measure | 🌐Source | ⬆️UP

function stantonMeasure(arr) {
  const count = n => arr.filter(x => x === n).length;
  return count(count(1));
}

Length and two values. | 🌐Source | ⬆️UP

function alternate(n, firstValue, secondValue){
  return Array.from({length:n}, (_,i) => i&1 ?  secondValue : firstValue)
}

makeBackronym | 🌐Source | ⬆️UP

var makeBackronym = function(string){
  return [...string].map(el => dict[el.toUpperCase()]).join(' ');
};

Frequency sequence | 🌐Source | ⬆️UP

function freqSeq(str, sep) {
  return [...str].map(el => str.replace(new RegExp(`[^${el}]`,'g'),'').length).join(sep)
}

Find Duplicates | 🌐Source | ⬆️UP

const duplicates = arr => [...new Set(arr.filter((el, i) => i !== arr.indexOf(el)))];

TV Remote | 🌐Source | ⬆️UP

const tvRemote = function(word) {

  let keys = 'abcde123fghij456klmno789pqrst.@0uvwxyz_/';
  let pos = [ 0, 0 ];
  let res = 0;
  
  for (let char of word) {

    let i = keys.indexOf(char);
    let dest  = [ i / 8 | 0, i % 8 ];

    res += Math.abs(dest[0] - pos[0]) + Math.abs(dest[1] - pos[1]) + 1;
    pos = dest;
    
  }

  return res;

}

Delta Bits | 🌐Source | ⬆️UP

function convertBits(a, b){
  var x = a ^ b, count = 0;
  do { count += x & 1 } while (x >>= 1);
  return count;
}

6 Kyu

Random Sequence Generator | 🌐Source | ⬆️UP

function Randomizer(min, max) {
  for (this.num = []; min <= max; min++) this.num.push(min)
  for (var i = 10; i--;) this.num.sort(function() { return Math.random() - 0.5 })
}

Randomizer.prototype.next = function() {
  if (!this.num.length) throw new Error('No more numbers')
	return this.num.pop()
}

Randomizer.prototype.sequence = function(size) {
  if (size > this.num.length || !this.num.length) throw new Error('Too many numbers')
	return this.num.splice(0, size || Infinity);
}

function Randomizer(min, max) {
  this.numbers = [...'0'.repeat(max-min+1)].map((_, i) => min + i);
  this.numbers.sort((a, b) => Math.random() - 0.5);
}

Randomizer.prototype.next = function() {
  if (this.numbers.length === 0) throw new Error('No more numbers');
  return this.numbers.pop();
};

Randomizer.prototype.sequence = function(size = this.numbers.length) {
  if (size > this.numbers.length) throw new Error('Too many numbers');
  return this.numbers.splice(0, size);
};

Arc Length | 🌐Source | ⬆️UP

function distance([x1, y1], [x2, y2]) {
    return Math.hypot(x1 - x2, y1 - y2);
}

function linspace(start, stop, length) {
    const step = (stop - start) / (length - 1);
    return Array.from({length: length}, (_, i) => start + step * i);
}

function arcLen(fn, range, intervals = 200) {
    const coords = linspace(...range, intervals).map(fn);
    const lengths = Array.from({length: intervals - 1}, (_, i) => distance(coords[i], coords[i + 1]));
    return parseFloat(lengths.reduce((a, b) => a + b).toFixed(2));
}

function arcLen(fn, [b, e]) {
  const n = 100000;
  let res = 0;
  for (let i = 0, pp; i < n; i++) {
    const p = fn(b * i / n + e * (n - i) / n);
    if (i != 0)
      res += Math.hypot(p[0] - pp[0], p[1] - pp[1]);
    pp = p;
  }
  return res;
}

Quantum Bogosort | 🌐Source | ⬆️UP

Array.prototype.qbsort = function() {
  this.qshuffle()  
  this.some((_,i,a) => i && a[i]<a[i-1] ) && QSC.destroyUniverse();
}

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