计数质数
解法一:暴力破解法
public class LeetCode_204 {
/**
* 暴力破解法:提交后超出时间限制,性能不好
* @param n
* @return
*/
public static int countPrimes(int n) {
int result = 0;
for (int i = 2; i < n; i++) {
if (isPrime(i)) {
result++;
}
}
return result;
}
public static boolean isPrime(int num) {
if (num == 2 || num == 3) {
return true;
}
boolean result = true;
for (int i = 2; i <= Math.sqrt(num); i++) {
if (num % i == 0) {
return false;
}
}
return result;
}
public static void main(String[] args) {
System.out.println(countPrimes(1500000));
}
}