最开始使用的算法
/**
*
* @param k质数因子个数
* @param start开始位置
* @param end结束位置
* @return质数因子个数为k的数值组成的数组
*/
public static long[] countKprimes(int k, long start, long end) {
ArrayList kPrimes = new ArrayList<>();
for (long i = start; i <= end; i++) {
long temp = i;
int prime = 2;
int pCount = 0;
while (prime <= temp) {
while (temp % prime == 0) {
pCount++;
temp /= prime;
}
prime++;
}
if (pCount == k) {
kPrimes.add(i);
}
}
return kPrimes.stream().mapToLong(s -> s.longValue()).toArray();
}
第二次尝试的算法
public static long[] countKprimes(int k, long start, long end) {
ArrayList<Long> kPrimes = new ArrayList<>();
for (long i = start; i <= end; i++) {
int t = (int) i;
int pc = 0;
while (t % 2 == 0) {
pc++;
t /= 2;
}
for (int l = 3; l <= Math.sqrt(t); l += 2) {
while (t % l == 0) {
pc++;
t /= l;
}
}
if (t != 1) {
pc++;
}
if (pc == k) {
kPrimes.add(i);
}
}
return kPrimes.stream().mapToLong(s -> s.longValue()).toArray();
}