Leetcode Count Prime

Description:

Count the number of prime numbers less than a non-negative number, n

Hint: The number n could be in the order of 100,000 to 5,000,000.

 

#define NO 0
#define YES 1

class Solution {
public:
int countPrimes(int n) {
if(n == 1)
return 0;

int num;
int count = 0;
for(num = 2;num <= n;num++){
if(isPrime(num))
count++;
}

return count;
}

int isPrime(int n){
int i = 2;
for(;i<=sqrt(n);i++)
{
if( (n%i) == 0)
return NO;
}

return YES;
}

};