Is a number prime?

Is a number prime?

Define a function that takes an integer argument and returns 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, depends on language version). 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 */

mov edi, 1
call is_prime    ; EAX <- 0 (false)

mov edi, 2
call is_prime    ; EAX <- 1 (true)

mov edi, -1
call is_prime    ; EAX <- 0 (false)

bool isPrime(5) = return true

Solutions

🐍 Python

def is_prime(num):
  if num <= 1:
      return False
  for i in range(2,num-1):
      if num%i == 0:
          return False
  return True

🧠 C++

#include <iostream>
#include <math.h>

bool isPrime(int num)
{

  if (num <= 1)
    return false;

  for(int i = 2; i <= sqrt(num); ++i)
    if( num%i == 0 && i != num)
      return false;

  return true;
}