Description:
Count the number of prime numbers less than a non-negative number, n.
public class Solution {
public int countPrimes(int n) {
int res=0;
boolean[] prime = new boolean[n]; //false:prime; true:prime
for(int i=2; i<n; i++){
if(!prime[i]){
res++;
for(int j=2;j*i<n; j++)
prime[j*i]=true;
}
}
return res;
}
}
