CodeWars: Weekly Newsletter

8kyu - positiveSum

The first question is to sum up all the positive integers in an array. Basically two things need to be done:

• Filter out Values that should not be added to the sum
• Sum up every item in the array

Basically you can write the solution like this:

export function positiveSum(arr: number[]): number {
	return arr.filter((val) => val > 0).reduce((total, current) => total + current, 0)
}

It is important to note that the initial value of 0 must be set, as if you pass in an empty array it would return NaN

7kyu - next Prime

Basically you need to check every number if it isPrime. Then you need to select an algorithm that can check if it is a prime number.

In this case I just took the code from the npm package is-number-prime. Which is a brute force way of figuring out if the number is prime or not. (There is probably something more mathematically elegant out there)

function isNumberPrime(n) {
	if (n === 2 || n === 3) {
		return true
	}

	if (n < 2 || n % 1 || n % 2 === 0 || n % 3 === 0) {
		return false
	}
	let foo = Math.floor(Math.sqrt(n))
	for (let i = 5; i <= foo; i += 6) {
		if (n % i === 0 || n % (i + 2) == 0) {
			return false
		}
	}
	return true
}

function nextPrime(n) {
	while (true) {
		n++
		if (isNumberPrime(n)) {
			return n
		}
	}
}