is-a-number-prime.md

Is a number prime? ^{6 Kyu}

^{LINK TO THE KATA - MATHEMATICS ALGORITHMS}

Description

Define a function that takes an integer argument and returns a logical value true or false depending on if the integer is a prime.

Per Wikipedia, a prime number ( or a prime ) is a natural number greater than 1 that has no positive divisors other than 1 and itself.

Requirements

• You can assume you will be given an integer input.
• You can not assume that the integer will be only positive. You may be given negative numbers as well ( or 0 ).
• NOTE on performance: There are no fancy optimizations required, but still the most trivial solutions might time out. Numbers go up to 2^31 ( or similar, depending on language ). Looping all the way up to n, or n/2, will be too slow.

Example

is_prime(1) /* false */
is_prime(2) /* true  */
is_prime(-1) /* false */

Solution

const isPrime = number => {
  if (number <= 1) return false

  const squareRoot = Math.sqrt(number)

  for (let i = 2; i <= squareRoot; i++) {
    if (number % i === 0) {
      return false
    }
  }

  return true
}