求100以内的质数，值得一看

Question

刚才看了一个招聘求100以内的质数问题，去求职的要求差不多都在7500/M以上，更有甚者要到12000/M,其实算法有很多种我贴出自己的算法，要价：4500/
public static void main(String[] args) {
for(int i=1;i<=100;i++){
int flag = 0;
for(int j=1;j<=i;j++){
if(i%j==0){
flag++;
}
}
if(flag>2){
continue;
}else {
System.out.println(i);
}
}
}

Answer 1

用素数筛选(prime seive)是很快的，空间换时间，时间复杂度O(nlog(log(n)))
[code="java"]
public void runEratosthenesSieve(int upperBound) {
int upperBoundSquareRoot = (int) Math.sqrt(upperBound);
boolean[] isComposite = new boolean[upperBound + 1];
for (int m = 2; m <= upperBoundSquareRoot; m++) {
if (!isComposite[m]) {
System.out.print(m + " ");
for (int k = m * m; k <= upperBound; k += m)
isComposite[k] = true;
}
}
for (int m = upperBoundSquareRoot; m <= upperBound; m++)
if (!isComposite[m])
System.out.print(m + " ");
}
[/code]