check_prime.cpp

bool isPrime(ll n) { 
   
    if (n <= 1)  return false; 
    if (n <= 3)  return true; 
 
    if (n%2 == 0 || n%3 == 0) return false; 
  
    for (ll i = 5; i*i <= n; i = i+6) 
        if (n%i == 0 || n%(i+2) == 0) 
           return false; 
  
    return true; 
}