class Solution {
public int solution1(int n) {
int answer = 1;
for (int i = 2; i < n; i++) {
if (isPrime(i)==1) answer+=1;
}
return answer;
}
private int isPrime(int n) {
for (int i = 2; i<=(int)Math.sqrt(n); i++) {
if (n % i == 0) {
return 0;
}
}
return 1;
}
public int solution2(int n) {
int answer = 0;
int[] number = new int[n+1];
for(int i=2; i<=n; i++) {
number[i] = i;
}
for(int i=2; i<=n; i++) {
if(number[i]==0) continue;
for(int j= 2*i; j<=n; j += i) {
number[j] = 0;
}
}
for(int i=0; i<number.length; i++) {
if(number[i]!=0) {
answer++;
}
}
return answer;
}
}