题解 | #质数因子#

1. 遍历到就可以结束了，如果此时数字还没有除数，则可判定其本身是一个质数，没有再除下去的必要了，直接打印其本身即可

2. string 转long

    String str = sc.nextLine();
    long num = Integer.valueOf(str).intValue();

3. import java.math.*;
   long k = (long)Math.sqrt(num);

import java.util.*;
import java.lang.*;
import java.math.*;

public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        String str = sc.nextLine();
        long num = Integer.valueOf(str).intValue();
        long k = (long)Math.sqrt(num);

        for (long i = 2; i <= k; ++i) {
            while (num % i == 0) {
                System.out.print(i + " ");
                num /= i;
            }
        }

        System.out.println(num == 1 ? "": num+" ");
    }
}