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/*
输出两个整数范围内的所有素数并且统计个数和所使用的时间
思路：
从2开始，到一个数-1结束，都不能被这个数本身除尽，则是素数；
可以用 isFlag表示是否被除尽，一旦被除尽，就break终止该循环；（优化一）
每找到一个素数后一定要重置isFlag的值进行下一次寻找；
从较小的数开始到较大的数，循环次数是 j * j < i或者j<=Math.sqrt(i);（优化二）
知识点：
long start = System.currentTimeMillis();
可以获得当时的毫秒数
*/
import java.util.Scanner; class SuShu{ public static void main(String[]
args){ Scanner scan = new Scanner(System.in); System.out.println("请输入第一个整数范围");
int x1 = scan.nextInt(); System.out.println("请输入第二个整数范围"); int x2 =
scan.nextInt(); int min = (x1<x2)? x1:x2; int max = (x1>x2)? x1:x2; boolean
isFlag = true; int count = 0; long start = System.currentTimeMillis();//记录开始时间
System.out.println(min + "到" + max + "之间的素数有："); for (int i = min;i <=
max;i++){ for (int j = 2;j<=Math.sqrt(i);j++){ if(i % j==0){ isFlag = false;
break; } } if(isFlag == true){ System.out.print(i + " "); count ++; if(count %
6 ==0){ System.out.println(" "); } } isFlag = true; } long end =
System.currentTimeMillis(); System.out.println(" "); System.out.println(" ");
System.out.println( min + "到" + max + "之间的素数有" + count + "个");
System.out.println("用时" + (end - start) + "毫秒"); } }
运行结果：
