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;

}



};