Questions.md

Multiples of 3 and 5

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

answer

multiples = b => a => !(a % b);
sum = (a, b) => a + b;
matrix = (a, b) => Array(a).join(',').split('').map(b)

matrix(1000, (x,a) => a + 1)
  .filter(a => multiples(3)(a) || multiples(5)(a))
  .reduce(sum, 0)

233168

Even Fibonacci numbers

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

answer

fib = (a, b, c) => a = c[b] = a < 3 ? a : (c[b-2] || 0) + (c[b-1] || 0);

matrix(10, (x,a) => a + 1)
  .map(fib)
  .filter(multiples(2))
  .reduce(sum)

44

## Largest prime factor

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?

answer

isPrime = num => {
  for(let i = 2; i < num; i++)
    if(num % i === 0) return false;
  return num !== 1;
}
isWhole = x => x === Math.ceil(x)
primeFactor = num => {
  let x = 0;
  a = [];
  for (let i = 1; i <= num; i++) {
    if(isPrime(i)) {
      x = num / i;
      if (isWhole(x)) {
        num = x;
        a.push(i)
        if (num === i) {
          a.push(i)
        } else {
          i = 1;
        }
      }
    }
  }
  return a;
}
primeFactor(600851475143)

[71, 839, 1471, 6857]

TURING(2019)!

const App = () => (
  <div>
    {'*TURING*(2019)!'.match(/([^A-Za-z*])/g)}
  </div>
);

answer

(2019)!

Find place of number in sorted array

getIndexToIns([40, 60], 50); getIndexToIns([10, 20, 30, 40, 50], 35) should return 3.

answer

``` function getIndexToIns(arr, num) { // Find my place in this sorted array. return arr.sort().reduce((prev, next, key) => { if (next < num) return key; return prev }, 0); } ```

Stream roll array

steamrollArray([1, [2], [3, [[4]]]]) should return [1, 2, 3, 4]

answer

``` repeat = (prev, next) => { if (Array.isArray(next)) return next.reduce(repeat, prev); return [...prev, next]; }

steamrollArray = (arr) => arr.reduce(repeat, []);

</details>

## Brackets

check("{()}[]") // true check("{[}]") // false

<details>
<summary>answer</summary>

const check = (text) => { let brackets = []; const pares = {'{':'}','[':']','(':')'}; const openBrackets = Object.keys(pares);

for (let i = 0; i < text.length; i++) {
	const currentBracket = text[i];

	if (openBrackets.includes(currentBracket)) {
    	brackets.push(i);
    } else {
		let test = brackets.pop();

		if (currentBracket !== pares[text[test]]) {
			return false;
		}
    }
}

return true;

}

</details>


## Write sum function

`sum(1)(2)(5)(10) // 17`

<details>
<summary>answer</summary>

const sum = a => b => c => d => b + c + d;

</details>


## Write five, add, one functions

`five(add(one())) // 6`

<details>
<summary>answer</summary>

one = () => 1; add = a => b => a + b; five = fn => fn(5);

</details>


## Write seven, subtract, two functions

`seven(subtract(two())) // 5`

<details>
<summary>answer</summary>

two = () => 2; subtract = a => b => b - a; seven = fn => fn(7);

</details>

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